Both platforms have it's pros and cons.
Personally I feel alt:V is rather more promising compared to RageMP, with it's continuous updates, better sync, helpful & great community and not too complex visuals & stuff. RageMP may have more users/players and bigger activity, that's mainly because there are more active and already largely developed (english) servers and it may have been around much longer than alt:V. Platform alt:V on other hand lacks many servers (lacks english ones, most are german there AFAIK), hence it has much less players and servers (pointing to unofficial statistics comparison above), but it does offer much simpler game joining than RageMP and writing a code is also equally easy to RageMP as well (my own experience), provided that people know how to code.
As far as I can see, the minds of which platform is going to be used has been already made up. Discussion between two platforms appears to be welcome here, but in the end, it might not matter too much at the moment, who knows what will happen in the future.