60 gun is better and can serve you until end game, so I suggest you get that instead. If you have the 50 bow right now, that is actually better at times than the 60 gun depending on match ups.
60 gun: zerks/pallies/wiz/necro
50 bow: rangers/sins
In terms of crystal damage then 60 gun all the way hands down.
60 bow is really just an overkill switch in once 50 bow activates. Although it is quite handy when you solo ACV as a sharpshooter.