I trade the NQ exclusively on IB everyday and am very happy. Instant executions and super cheap commissions. ($4.80 roundtrip). I used to trade only stocks with IB before the new margin rules, and the executions seem to be just as good with futures vs stocks.
As far as reliability goes; I'd give them a 9 out of 10. When TWS is up and running it's perfect, but every once in a while the screen will go purple and everything freezes up. It reboots itself within a few seconds generally. It's kind of a pain but considering all the other benefits I'm not complaining.