I have been to a few different conventions. Â I have seen varying degrees of quality in them. Â I was JUST at AX2015 on July 3rd and it was awesome! Â It wasn't just mainstream appeal, they had all sorts of offshoots. Â I have went nearly every year since they began and the only real issues I have run into is lack of organization. Â I have had years where the lines to pick up your badge took 2+ hours to get through. Â This year, they seemed to have pretty much nailed it though.
At smaller cons, you get the feeling that you're at someone's birthday party or something, and it can be very awkward. To be with a bunch of other anime obsessed folks in a group that is large enough to stand out, but too small to matter is an icky feeling. Â I've also seen these "indie" cons grow into major events and be awesome, so they are not necessarily bad.
All in all, treat it like a baseball game: Â Bring lots of money, expect large crowds, try not to get into arguments.