Lots of good info already stated here, so I'm not sure what I can add.
I don't remember making any real choice of single stage vs. progressive, probably because I didn't know enough about either type to make an informed decision. I got a 550b because it appeared to be well-designed, and relatively simple. I think I got lucky, in other words.
It took me quite a while to get it running correctly, and then a while longer before I ran it in full progressive operation.
Without any advice from others, I decided to run it "one cartridge at a time" until I had faith in the machine and my process.
While I don't believe I have gone far enough to be classified as complacent, I would admit to being "comfortable" with it after 10 years.
I suppose I would agree that perhaps a little more mechanical aptitude and patience is required to run a progressive. I will confess to being an engineer, and I am aware that an analytical approach to things comes naturally to me. However, I have worked with many individuals who find that approach completely foreign if not abhorrent.
Also, while a progressive press may allow a beginner to make mistakes 10 times more quickly than he could on a single-stage press, I'm not convinced that a single-stage press is any
guarantee of safety. Sloppy process is dangerous, regardless of the equipment being used.
So, I would agree with those who say a beginner could start with a progressive press, provided due caution is exercised and appropriate time is allowed for setup and "working up the learning curve". If, after consideration, the beginner feels he doesn't have the time for this, then perhaps a single-stage press would be better.
(But I still have reservations about recommending any kind of reloading equipment to someone who says they are in a hurry...
)