Only really started watching NXT sporadically when the Takeovers started. What are the best matches from this group from its start in 2012 up through the end of 2015?

Your mileage may vary on what you call "top tier", but poking around for a general consensus yields the following list:

 

Kassius Ohno vs. William Regal 4/10/13

Antonio Cesaro vs. Sami Zayn, 2 out of 3 Falls 8/21/13

Antonio Cesaro vs. William Regal 12/25/13

Cesaro vs. Sami Zayn 2/27/14

Charlotte vs. Natalya 5/29/14

Adrian Neville vs. Sami Zayn vs. Tyler Breeze vs. Tyson Kidd 9/11/14

Charlotte vs. Sasha Banks 12/11/14

Adrian Neville vs. Sami Zayn 12/11/14

Adrian Neville vs. Finn Balor 2/11/15

Bayley vs. Becky Lynch vs. Charlotte vs. Sasha Banks 2/11/15

Kevin Owens vs. Sami Zayn 2/11/15

Becky Lynch vs. Sasha Banks 5/20/15

Finn Balor vs. Kevin Owens 7/4/15

Bayley vs. Sasha Banks 8/22/15

Finn Balor vs. Kevin Owens, Ladder 8/22/15

Bayley vs. Sasha Banks, Iron Man 10/7/15

Finn Balor vs. Samoa Joe 12/16/15

I would add to that list:

 

Neville vs Harper - 21/02/2013

Cesaro vs Sami Zayn - 13/06/2013