In my opinion, the larger conferences tend to be a complete waste of time -- they're basically a time for press releases by vendors who want to sell you something. You get the same thing with the mid-sized conferences in the D.C. area with the 'free for government employees' conferences.
My preference is towards mid-sized conferences (under 1000 attendees), where you actually have a chance to get to talk to people and do some networking ... of course, employers don't always like these, as part of the networking may be your finding another job elsewhere.
Really small workshops (20-200 attendees) are very educational, but they're so small that there's generally an expectation that they're more about collaboration and discussion. I've been to a few that were either 'by invitation only' (typically my boss is invited and sends me in his place; for one I talked my way into an invite; another required everyone to submit an abstract and they selected ~50 people to attend based on them). They tend to be strategy related -- what issues does the community need to be aware of & working on.
You also have the more 'academic' vs. 'practical' conferences in some fields ... the academics present on research but often end up missing what I believe are the really key questions that they need to be asking. Practical conferences can also be tiring, if you end up with talk after talk of people coming up with effectively the same solution to a given problem.
From the sounds of things, what you're looking for is training, not conferences. Some conferences do offer training either before, during or after the conference ... and for the pre- / post- stuff, you may not need to register for the main conference.
As for who pays ... it depends. At my work, training is handled seperately from conferences ... for conferences, I get reimbursed for my expenses (travel, hotel, food, registration). For training, I get registration back (provided it meets with their requirements for 'training', but not the rest of it unless it's 'company directed training' (they told me to go, vs. my asking to go). In many cases, I've worked with my manager to get listed as 'teleworking' during the conference, so they'll pay my salary while I'm there, but I pay the rest of the costs.