Another issue I heard of regarding the SRC G36s is the hop up unit, something about irregular gap which leads to possible air leak. But between the two I'd still go for the G36C.
The need of a riser mount really depends on your face protection. It's likely that you'll need one if you wear a bulky paintball mask.
BTW, have you considered KWA G36C? Their 2009 version is pretty awesome and is full black.
