if you plan on one caliber only for pistol, get a square deal. if you plan on or there is the possibility of multiple calibers in the future, get a 550. i have a sd set up for 44 mag and a 550 for 45 auto, 357, 30-30, 223 and a few others. i have bought 4 dillon presses and like was said, that is the way to do if because dillon backs it whether you bought it new or used, it just doesnt matter.
if you are not in a hurry, look for a used one. if you are, dont feel bad buying one new, they are worth every penny. you simply cannot go wrong with a dillon press.