I don't think either engine is well suited for an MMO to be honest. You are probably better off looking at something like the HeroEngine.
Unreal Engine's built in networking systems are suitable for 64 players, maybe 128 tops. It's replaceable, but I wouldn't recommend delving into that.
I will say this though, if you have 1 C++ programmer with UE4, they can create functionality not builtin to the engine and expose it via Blueprint (the visual scripting language) for non-programmers to use. Blueprint is a fantastic and very easy to use tool. Take a look at the forums to see the incredible things people have built with ZERO programming knowledge.