It's pretty subjective really - what's more important: venue, soundsystem, dj roster, crowd, or geographic location (Space would be nothing if it was located in Hackney!)?
I think Ibiza clubs are still the best for the following reasons:
1. Everyone there (with a couple of exceptions) is on holiday, so the atmosphere is always awesome (and messy)!
2. Sunshine! Nothing beats dancing in the sunshine to quality house music
3. The DJs - petering of in recent years, but I still think it's name as the 'DJ mecca' of the world is justified.
Having said that, I've yet to go clubbing in Miami or the West coast of the USA.. although most of my american mates like the crowds in europe more..