The best BTC Web wallet is http://blockchain.info 
There are some others Web wallets too, but blockchain is most popular walet 
There are some others Web wallets too, but blockchain is most popular walet Anyway, to answer you question, blockchain.info is imho the best one
... for committing economic suicide.
sure, that it is stupid even think about using of it, but OP asked about web one and I really hope, that after all those hacks is everybody smart enough to decide, if use web wallet or not..