What Ron said - agreed. Everything he wrote is spot on.

I will definitely be at Origins and quite likely at Gen Con. After a number of
classes at GC, I would recommend trying painting classes at both if you have
that option. Origins classes are intended to be a different style & approach
from those at Gen Con. Not competing against them, not better or worse, just
different. Metaphorically speaking, you could say that if Gen Con classes are
ice cream, then Origins classes are frozen yogurt. If you can do so, try them
both and decide what works for you.

Shameless plug for Origins: I will be teaching several classes and would like to
see everyone's full, not just mine. Mine may or may not be what you are looking
for - Prepping Minis, Intro to Painting, and Animal Colors & Patterns. The
first two are intro-level and hands-on, the other is more verbal & textual.

Again, like Ron said, sign up in advance if you can. If not, take generic
tickets and see if you can slide into a seat from cancellation or no-show.
Above all, have fun and absorb what you think will help you enjoy the hobby
after the conventions are over.