Don't forget MarketFeed. In my opinion, they are the best level I quote provider for QT....I tried StockWatch for about 1 day and cancelled. Datek is OK for a backup....
As for Level II, I use Datek...but I don't really need Level II for my trading style, which is why I don't feel a need to pay a premium for that data. If I was going to pay for Level II and continue using QT, I'd definitely go with MarketFeed....