I'd go with the Logitech G502, simply because Razer's are something I'd avoid after owning a couple and them failing in spectacular fashion. You could look into Roccat's lineup or Kingston's or even from Corsair.
I can't say much about the new Razer mice (aside from the Naga line that I have used for a long time), but I had a death adder back when they first introduced the line (10 years ago or so), and it was a very comfortable mouse. That being said, what makes you debate between these two particular mice? I have a couple Corsair mice myself, and so far they have been fantastic. Also have to remember, sometimes more buttons isn't always the best thing when it comes to a mouse. It can be nice, but sometimes, depending on the person, you may find certain buttons awkward to use depending on how the mouse fits your hand. Have you held, or used these two mice before?