Get whatever is the cheapest, reliable, version of THE SAME RETICLE AS YOUR BIG/COMP RIFLE. The idea of a trainer rifle is to duplicate, as closely as possible, your big/hunting/comp rifle right?
Then do that. I think as long as the reticle is the same then the rest kinda doesn't matter as long as you aren't trying to use a semi-auto as your "trainer" for a bolt gun or whatever.
-Doc