I myself have won a lot at 888 poker. It's a good bankroll builder.
My method is that I win some cents at a normal freeroll, than win one or two 2 cent Sit & Gos and than I often try the Double Or Nothing for about 0,55$.
At 888 Poker you can make a bankroll starting from 0$.
But at Pokerstars so far I don't won one. I think because much players are at the tournement and also nine players at one table, not only six like at 888.
At Pokerstars you also can't really cash in freerolls
, maybe it's more suitable for a depositer.