550B
I have one and load .45, .40s, .357, and .44Mag in it. I average about 8,000 rounds a year shooting IPSC with my son so I get a lot of press time.
If I were shooting a few thousand a year, I would buy a 550 again without question. As our shooting has increased, it would be nice to have the 1050 -- for about 4 times the cost -- because you can load so darned many more per hour with some additional bells and whistles. That is at least 4 times the cost, however. I know several folks who like the 650 a lot, but I'm not sure how much is gained by it.
I'm compulsive about checking things as I reload, and I don't rush; I figure I can run about 250 rounds out in an hour at my pace. I know many who load much more than that.
I would not buy ANYTHING but a Dillon, personally. I have firsthand experience with their no bull**** warrantee. If something isn't right -- any time, anywhere -- it gets fixed. I got a FedEX package with the part, no questions, no charge. To me, that's worth a LOT.
My primary interest is in handguns, but if you consider something smaller like the Square Deal mentioned above, be advised -- it's ONLY handguns. If you have ANY potential interest in rifles, get the 550 or greater.