I'd have to say iPhone, I've been let down with every WM phone I've ever had but not used android a massive amount.
I've worked in the mobile business, used hundreds of handsets over many years and for me the iPhone is my favourite handset ever.
If you want a nice looking phone to play games on, watch vids & don't mind charging the damn thing every day you'll be mnore than happy.
O2 stores all have demo iPhones to play with, Tmob tends to have the G1 to play with so try them out, the problem with this sort of question is 'it depends...'