I've actually had (have) both. I loved my DeathAdder while it lasted, but for whatever reason.... Razer mice break after less than a year for me. The one that lasted the longest is my Copperhead, which went for 2 years. And it's not like I'm swinging my mice around, almost every Razer mouse has a key issue that makes it go bad after awhile. For the DeathAdder, the left click went kaput. I did some research and a lot of people had the same issue. So I dunno, I switched the the G500 and so far, so good.
But survivability shouldn't be the only thing I judge on I suppose. Honestly, the DeathAdder glided real nice while I had it. It worked very well for me, but it was always a little light. The G500 is a very sturdy mouse, and you can adjust how heavy or light you want it to be. The only issue I've had with it is that the programmable keys have some odd other functions too, such as minimizing my windows. It only happens sometimes, so it's not a huge deal for me.
I'd go with the G500, but it's your call.