Ambit peak 3 sapphire. I have used this thing for training 5+ days a week for 3 years, including multi-day backpack hunting/skimo/powder trips and have had no glitches, and it has held up well. Aside from training it is a really good tool for mountain navigation and maintaining pacing for big fast days. The ability to program custom sports modes is a huge pro for me, you can program custom modes to save battery life and storage space so you can log multi-day tracks without recharging, or program modes for specific objectives so you can estimate your pacing for a particular route.
The Sapphire is worth the extra $$ if you are going to do any type of climbing around rocks or use the watch on extensive backcountry adventures.
Overall its a huge investment, but if you are going to be getting really serious about training it is certainly worth it, and, having a mini GPS on my wrist logging my location has saved me from some uncomfortable nights when animals have led me far astray from my intended path...
Finally, I would strongly recommend using a chest strap if you are serious about aerobic training, the non-strap options are O.K. for casual use, but chest straps are still the gold standard for training tools.
