I'm sure you'll hear both sides - in general, I prefer a bolt gun for both daytime hunting and thermal at night.
An AR is definitely nice for quick(er) follow up shots, but I feel I'm better with a bolt gun (probably from doing 98% of my shooting with one). I have an AR in 6 ARC I've been using for thermal lately and it's been a lot of fun.
Depends on if you are a one shot one kill guy or a mag dumper. Some folks call in two, kill one, then dump 20 rounds at the other as it high tails it outta there. They like AR's. If you like to wait till they stop then kill them, a bolt is fine.