There's always SRM $$$
In all seriousness, anecdotally the SRM, Quarq, and PowerTap devices are the least problematic of all devices I hear about. Ironically, as Tonka has pointed out, the one device I would have trepidation trying would be the Garmin vectors, I'm not too fond of the design. In all fairness, that's the main reason I wouldn't choose them, plus I hear the calibration process is cumbersome. However, I wouldn't hesitate to try the 4ii, Power Tap, Power2Max, and Pioneer systems. I personally (and luckily?) have used Stages with great reliability and durability, despite what others have found.