Is this a trick question?
Seriously, you'll find that having two presses is useful. I'd buy the Dillon because you'll be much happier with it as a progressive. You can set it up for the major caliber you reload for and use the Rockchucker for the occasional 10 or 20 rounds of hunting ammo, etc. I own both and wouldn't have it any other way. In fact, I'm debating whether I should add a second 550B to my menagerie.