I've been using IQFeed and Ensign for a few months, primarily for the eminis. It's been very reliable and the ES, NQ and YM data are clean and timely. And it works in Quotetracker as well, which is awesome (thanks again Jerry, your program is great!).
They do not, however, have continuous contract symbols, so that's been a bit of a pain...I asked them about this and it doesn't look like it's in their plans. And when looking at stocks, I seem to get some errant ticks, though these could be either bad data or just out-of-the-market prints that need to be filtered...hasn't caused me too much grief, I just filter. There is also currently some issue between Ensign and IQFeed that shows up when you are getting alot of activity in ES and you have a Time & Sales window up...Ensign continues to graph and the time&sales rolls, but it stops being responsive to mouse clicks which can be sort of a pain. Supposedly this is a known issue and is being fixed.
I've recently started watching the ESTX50 on EUREX as well, and that data is ok, but missing volume and lags by just about 1 sec from IB...but otherwise appears pretty consistent. I haven't followed up with them on the volume issues yet.