Which LMS do you use and why?

We currently use Absorb by Blatant Media.  We have a pretty huge user base with over 16,000 users.

I have gone through two other LMS implementations, and was willing to drop them and change and so far Absorb seems to be our favorite.

I can tell you this though.  There isn't a perfect one.  You just want to find one that meets most of your needs, then be prepared there will be errors, and bugs.

The two common factors in all of our endeavors is the Articulate suite.  Articulate is awesome and there really isn't anything out there that we have found comparable, but part of the bugs we have to look at might not just be the LMS provider it may have to be with how a published Articulate course or quiz works within the LMS.

And then you have the ever changing, ever updating Adobe flash player that gets updated every week.   Sometimes we have courses that work perfectly, then Adobe comes along and does one of their updates, and a course goes haywire.

Be prepared.  There will be errors.  There will be complaints.  There will be bugs with all LMS providers.

Just be very clear on your outcomes and needs, and then go for it.

Hope that helps.