Good question
My favorite of the bunch is Buddy. That's not a knock on the other two, but I'm not sure I could name three guys I enjoy watching more than Rose. I'd take Blackwell easily over Patera in terms of who I would rather watch, so from that perspective it is Buddy, Jerry, Ken.
As HoF candidates?
Well I'll look at the unique advantages of each guy briefly, followed by looking at where they are weak.
Jerry Blackwell Pros - Of the three Blackwell is the only one who was the top draw of a territory that was doing no less than 5-6k in every major building it was running, with multiple 10k plus/sellout runs to his credit. He is also the only one who was both the top drawing heel and top drawing face of the territory doing that sort of business in the same year. He was a more important part of a super hot run than either Patera or Rose were, the "MVP" of the AWA from 80-84 according to two of the three most knowledgeable AWA fans/historians on the web. Of the three Blackwell is the one where we have numbers that show trends of business slipping in his absence and spiking upon his return. He was most certainly the best worker of his size from the era for whatever that is worth and other than Vader I struggle to think of another super heavyweight better or even on his level.
Jerry Blackwell Cons - His entire candidacy rest on his AWA run, particularly from 80 through the middle of 85. This was a hot period for wrestling and though AWA haters/Blackwell deniers are spinning their wheels when they try and argue Blackwell wasn't a draw and a massive part of the AWA's success, Blackwell was not a top ten star in the States during that period, and it can't conclusively be shown that he was a top ten draw during the period either. Guys with comparably "brief" but hot runs, who were more obviously "aces" like Tommy Rich and JYD haven't even been on the ballot, and both could be argued as "more deserving." Though he was a star in St. Louis too, he was not really in demand anywhere else and was a mid-carder at best everywhere he went before his AWA run.
Ken Patera Pros - Easily the most in demand of the three, Patera wrestled everywhere as a top of the card wrestler from the early 70's until he went to jail in the middle of 85. He worked programs in money making slots on the card against nearly every major star of his era including Billy Graham, Bill Watts, Bob Backlund, Andre The Giant, Dusty Rhodes, Wahoo McDaniel, Hulk Hogan, Jerry Lawler, Tommy Rich, Tony Atlas, Pedro Morales, Bruno Sammartino and main evented multiple times in virtually every major wrestling town in the United States and Canada during the same run. Holding the I-C and Missouri titles at the same time seems like a kayfabe accomplishment but is a good illustration of his relevance at the time. Of the three Patera is the only one that started off his career near the top of the heap and didn't really fall from that perch until after his release from prison.
Ken Patera Cons - Even at the height of his value and drawing power, Patera was never the ace or top draw of any company he was in, nor was he a staple of cultural significance to a particular territory. It is arguable that he was not even the top heel in the WWF during his hottest year, though I would view that as a stretch. For these reasons Patera is forgotten or remembered as the shell of his former self that he was after he got out of jail, a perception that is hard to counter since that was the only Patera that many modern fans know. Though he was not a bad worker, and at times was great, he was not anywhere near as consistent as the other two and would not be considered anywhere near the top of the heap in that regard when looking at wrestlers from that period.
Buddy Rose Pros - Of the three Buddy is the only one who can say he holds gate records in every town on the loop he worked and obviously is the only one who can say he was the best draw in the history of a territory of note with a seventy-plus year history. On top of being the best draw in the history of Portland, he was also the best worker in Portland history. He was well regarded as a great in ring performer during the era and we now have more than enough evidence to support this. In my view he was the best worker in the world from 77-84, and of people I know who have seen big chunks of relevant footage from that period no one has seriously disputed this. Unlike Patera and Blackwell who were drawing well and having high end matches with some of the most talented names in the business, Buddy was holding the fort down, having great matches and setting records against a variety of green, over-the-hill and/or outright shitty performers with no true consistent "second" (like say a Dundee in Memphis). He is the only one of the three that was the top star and draw in two promotions at once (Portland and San Francisco). When Buddy left things were never the same in Portland and attendance plummeted which is evident if you watch the footage.
Buddy Rose Cons - Has the same perception problem that Patera has as he is remembered by some solely as the guy from the "blowaway diet" bit. The fact that he never worked for any length of time during his prime outside of Portland leaves him with the rep of a homesteader who was a "big fish in a small pond." It's possible Rose only worked in front of 10k plus audiences a couple of dozen times in his career and he was likely only on top of those cards a handful of times. Though he was the top draw in Portland from the time he took over the lead heel role in 76, until his last big gate match v. Piper at the Don Owen Anniversary show in 85, his run as a top guy is not incredibly long, and after his stint with in the AWA ended in early 87 he was never really relevant in the business again.
I would vote for all three guys. If I am being honest and weighing all things I think Blackwell is the least of the three, because of the brevity of his run and the fact that outside of St. Louis (where he was more of an semi-main guy, than a main guy) he wasn't a star anywhere else.
Between Rose and Patera I think it is a really tough call.
Rose has some advantages that are tough to factor in. Yes Portland was small, but he was the ace, he was working very limited talent and yet he was biggest act in the history of a promotion that was financially viable for years. The matter is really complicated because of Don Owen's business model - particularly the fact that he owned his own building. The lack of attendance figures from Portland makes it tough, but it is possible - probable if we guestimate based on the footage - that there were weeks were Rose was main eventing two shows in the PSA each drawing 3k plus and starring on a television show that did massive looking ratings. Buddy was a cultural fixture in a way that Patera wasn't anywhere and few wrestlers have been. He was a much better worker than Ken, to the point that even in Ken's best year (1980) I would struggle immensely coming up with a case that Patera was better.
Having said all that if I only had one choice between the two I would pick Patera for one simple reason - every other wrestler with the range of success in programs with names that big and towns/territories that broad over a span of time that long is in. The only possible exception would be Hans Schmidt and he should be in and I believe will be in this year. Patera has twelve years of being an in demand drawing card against the biggest names, in the biggest buildings, all over the country. Someone like that really belongs in the Hall of Fame unless he has some sort glaring negatives that cannot be ignored which Patera does not have.
Buddy is almost a project in and of himself to see how we are supposed to view an utterly unique candidate. A guy who was a great, record setting, best in the history of the territory, draw in a promotion that didn't often run major venues. A guy who was a cultural figure in a town that wasn't terribly big at the time and was remote from the rest of the wrestling world. A guy who was regarded as one of the great workers of his era at the time, but no one really saw the footage believing it didn't exist and now many won't watch or seek out the footage because it was "just a little pond" or "you can't get an accurate look viewing things out of context." He really has no point of comparison in some ways, though I would guess the Brit candidates are the closest (for the record I'd vote for Jim Breaks if he were on the ballot and I had a vote...I think).
Patera should be in because he meets and exceeds the criteria that has generally been accepted as standard for HoFers.
Rose belongs in to but he it will require a lot of thinking outside of the box to get him there.