I've had two Spektrum DX7s (The original units) for some six years. One was used continuously as the primary transmitter, the second retained as a backup unit. Never had to use the backup unit.
These transmitters were flown with genuine Spektrum receivers, with solid receiver power. Receiver power is either Castle Creations 10 Amp uBEC, or a 10 amp uBEC along with a backup two cell A123 battery pack on my giant scale models. Never once had a glitch.
One guy in our club had a problem with his Spektrum DX7, losing bind once and awhile. Spektrum couldn't reproduce it. So Spektrum returned a BRAND NEW DX7 transmitter. Pretty common service by Spektrum.
Just about everyone in my club that has gone to 2.4 Ghz has gone to the various Spektrum radios. Spektrum has their "Model Match" feature that absolutely prevents you from taking off your model with the wrong model in the transmitter. If your transmitters active model doesn't match your model ready to fly, that model is dead. Nothing moves.
I've sold one of my DX7's to a club member who is still flying it. It was replaced with a brand new DX8 transmitter that also has been flawless. And, the DX8 is much easier to program for dual aileron, dual flaps, dual elevator servos than the DX7 ever was. Took me 5 minutes to program this in to my giant scale, and didn't even need the manual.
As for popularity of the various radios, take a look: