I've been using a Dillon 550 for about 15 years, but I'm looking hard at a Hornady Lock-N-Load. I frequently have problems with the primer bar jamming because of all the primer debris that gets into the mechanism. Still, it's a good machine and I suppose all the brands have their quirks.
When the machine was young I had some good experiences with Dillon's customer service. However, I recently bent the decapping pin on a Dillon die and they made me buy a new pin (actually a pack of ten for a few $$ more). Based on past experience and reading other's writings, I really expected them to replace it for free. It was my fault for bending the pin, so I really shouldn't complain.
Anyway, I recently stumbled on this comparison of the two machines. I'm afraid I have to agree with many of the faults found with the 550, though not all.
http://www.cs.odu.edu/~rtompkin/hornady/blue.php
http://www.cs.odu.edu/~rtompkin/hornady/blue.php
I saw one guy in another forum complain that the Dillon makes you use both hands for handling components (left hand for bullets and right hand for cases), whereas the Hornady allows you to leave your right hand on the handle. I actually like using both hands because I can insert a new case and place the bullet almost simultaneously. It took a few thousand rounds to get the hang of it, but I can do it my sleep now.