Not sure why I'm stuck on warranties, but maybe cuz I've had to use them before...
If you buy new, most companies have a pretty good warranty, but if you're going to buy used only a few companies cover used guns. Springfield and STI come to mind as the most obvious. Colt and Kimber, for example, cover only the original purchaser.
You really should decide on particular features you want and then go looking for the gun that fits the bill.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face