I have a Hornady LNL AP. I also have the predecessor to the Dillon 550, the older 450. I like the 450 for what it does; it's a 'semi-progressive' press--I have to manually turn the shellplate to move the 4 cases to the next stations. I've used the 450 to reload about 12,000 rounds of 45ACP, and maybe 300-500 rounds of each 9mm, 38sp, 357, 44Mag, and 50 AE per year. I also use the 450 for .308 Winchester. The Dillon works very well except the powder drop is completely undependable for accuracy work. I could never get the Dillon to drop better than +- .2 gr of WW231 or 700X; that's pretty bad when the entire load calls for 4.6 gr. It was horrendous with any extruded rifle powder, dropping anywhere from +-.4gr in a 40-44gr load. This was after numerous calls to Dillon yielded new replacement parts and advice. Out of frustration, I finally gave up, and Rube Goldberg'd my own powder drop system onto the 450, using a Lyman 55 in conjuction with a PACT scale. My experience is that the Dillon is probably a fine press for hurrying out steel plate ammo, but I wouldn't keep it for a paperweight if accuracy is the main consideration, and time isn't.
I found myself doing the same research you are in a search for another (fully progressive) press. My choices were Dillon 550, Hornady LNL AP, and the RCBS 2000. I settled on the Hornady because I could get a Fully progressive, 5-station press with a highly recommended powder dispensing system for $100 less than a semi-progressive 4-station Dillon with its' powder measuring problems. In the end, the whole setup (not including reloading dies) ran me $586 for 5 caliber changes (including the necessary 20 bushings, 4 of the cheaper, 'common' powder die changes and 1 micro-adjusting rifle powder die and 5 drop linkages) and an RCBS lockout die (it works out to a lot less than $50/caliber if you only buy the required hardware). $586 won't come close to 5 caliber changes and a 5th station with the Dillon 550. I can switch calibers and start reloading in a maximum of 45 seconds (how long does it take to turn 5 dies a 1/4 turn?). Without a case feeder or primer feeder, I can maintain a steady unhurried pace of 300-350 rounds an hour, 400/hr if I'm in a hurry. The Hornady LNL and its' powder measure yielded .308's capable of .5MOA from my M1A, even with IMR 4064 (+- .15gr drop). (I had entertained the idea of eliminating the Dillon 450 for the table space, so I experimented with the LNL and .308 reloads, but decided later against that idea because changing for .308's required adjusting the Redding dies for OAL, and I just didn't want to go through the hassle, so I left the 450 set up permanently for rifle.
Some reloaders have complained about the priming system; I was one of them. I had horrific problems that turned out to be my fault--I wasn't swaging MilSurp brass enough to dependably accept the primers, and we (the Hornady tech and I) didn't figure it out for months. It is said that Hornady has revised their priming system for the LNL AP; I note that as a rumor, as I haven't seen a new press in real life. There were 3 complaints (outside of my swaging problem) that I can think of with the Hornady--some users had problems with the primer feed slide. This was remedied by beveling/polishing the underside of the slide slightly with a Dremel to insure smoother sliding. Secondly, some reloaders (including me) complained that the primers sometimes got stuck in the primer tube. This was cured by installing a ramrod-like weight into the primer drop tube (like the Dillon 450 has). Lastly, some of the very early releases of the LNL AP (mine was one) were sent out with "first edition" user manuals. These manuals inadvertantly omitted two pictures in the primer-feeding setup instructions, and that made the priming system even more of a mystery for those that didn't call in (like me) until desperation set in. I understand that editing problem has been cured.
All in all, and without compromising, I regard the Hornady LNL AP as the desirable premium press in the 550/650/LNL AP/ 2000 class. Dillon has its' following, and Hornady will probably never outsell them, but I liken these OEM's to the old Beta vs. VHS wars. (Beta was way better, but savvy marketing sold the VHS format.)
Widener's will ship it for free if you spend >$100, and their prices are very competitive.
Here's a link to some reviews by others:
http://www.thefiringline.com/forums/showthread.php?threadid=104226&perpage=25&pagenumber=3
