I've had a naga epic for a long time and haven't had any problems out of it aside from a sticker peeling a bit, nothing mechanical/electronic though. The only problem I've had out of it is that when the battery gets low tracking gets really wonky and unfortunately the battery life isn't amazing, maybe 6-8 hours of continuous use, though I'm sure if you turned off the LEDs you could squeeze another half hour-hour out of it, depending on what you consider to be 'continuous use'. I'm not sure what the range is like but it was sufficient to leave it on my entertainment center and play from my couch without any problems aside from the aforementioned wonkiness near the end of its battery life.
The Naga '14 looks like a solid upgrade but with new hardware comes the possibility of them cheaping out which they've been known to do on their other lines. My two nagas (G1 and Epic, bought epic for wireless but my original is still 100% fine) have lasted me basically since I started PC gaming so I don't really have any experience with the others that have been mentioned here. When my epic dies I'll probably go back to my G1 and when it dies I honestly see myself getting a new naga, I love both the ergonomics and the extra buttons, the only thing I'd change is MB 4 and 5's placement which has been bad since the start. --- Every time I try to go where I really wanna be it's already where I am, 'cuz I'm already there XBL, PSN, Steam, Origin, BSN, GFAQs, MC: PhilOnDez