Being a UK player I've stuck with the more euro-friendly sites:
Coral Poker (Ongame Network)
Paddy Power Poker (iPoker Network)
PKR
Poker Heaven (Boss Network)
William Hill (Cryptologic)
I've tried virtually all reputable networks but I am definitely with Egan Towst in that having over half a dozen live accounts with different sites becomes a nerdy balancing act and then just a headache.
If you spread your
bankroll around thinly on many sites, you just win or lose piddly, almost meaningless amounts; the gains just become VERY LONG TERM and it can all seem like a bit of a chore.
By honing your skills on 2-3 "favourite" sites with a more meaningful bankroll (and keeping 1 or 2 sites just to "knock around in") then the pay off is a bit more significant in my opinion.
Like Egan Towst, I generally play a lot at one site (PKR is my current choice as it is very lucrative for me) and hop into 2-3 others on a regular basis. William Hill is one I dip into only occasionally because the players seem a tad tougher.