I have the nGauge from Lund Racing.... Love it so far and the tune! It really depends on the tuner you are going with and what they are comfortable using.
Yeah. Cost is a factor as well, the SCT X4 tends to come in a little cheaper and everyone does use it. It is more fiddly when changing tunes or datalogging though.
Lund nGauge does not use HPtuners, so be aware of that. They use their own software. The firmware updates on Lund's site only works for theirnGauge as well. Found out the hard way on that one. xD
I bought mine from MPT, which use HPTuners. I absolutely love my nGauge, especially because of the fact that both my vehicles are supercharged, so I like having a quick way of checking the system. On my 4 PID read out, I have AFR, IAT2, boost, and engine coolant temp. I then have my LEDs showing my knock adv/ret, so I immediately know if the truck is doing anything dangerous.