What kind of game are you making? Ren'Py is basically exclusively for VNs, so if you want to talk about graphics then Unity is better and Ren'Py isn't even competing. If you're talking about pc performance then Ren'Py wins unless the developer figure out ways to write extremely pointlessly wasteful code since Ren'Py is scene based and doesn't normally need to bother with fps or update cycles.