I've been to 2 in London and 1 in Birmingham back in 2008-2009, and recently attended a few local one's here in North Wales. I can't imagine going down to the the big conventions nowadys as I'm sure the amount of people who attend have doubled or tripled! Like Cube, I enjoy the casual nature of the smaller local con, plus I don't have to book train tickets or a hotel
Had a lot of fun at Wrexham on Sat. Cosplayed as Han Solo and shouted out "Ben!" whenever I saw a Kylo Ren cosplayer, met Veronica Taylor, the voice of Ash Kethchum and Xander Berkley, 24's George Mason, attended some interesting panels and enjoyed browsing the stalls, identifying cosplayers and playing a few video games.
Some pics :-