I think Sora would be more fun, since so many people expect you to do axel. I like the sneaks of Sora that we've seen, and if Sora was given more time in the limelight im sure others would agree, but for now Axel has been dominating, which is why he is loved more. Hey, im not saying im not a fan of Axel, quite the opposite infact... I prefer him to Sora in the game, and through what you have done for him too.
Since you are doing them both equal, i'm sure you will see for yourself who people prefer when it comes to the expo. And you've done it like a rock concert; have your new stuff at the start, and then show what is your 'hit' at the end..... I despise you for that cause now i am wanting to attend both days instead of just going to london for the day and then going home XD.
Haha yeah, I'm right in the mix with everyone else here. I love your Axel cosplay, and I'm an Axel fangirl in general, so he'll always win out, especially when someone does him as well as you do. HOWEVER, you make an incredible Sora, too. So, my grand conclusion is: play with both, 'cause you look amazing in either.