CS:GO
I play a lot of CS:GO i have over 2.100 hours in CS. CS is a very good game it's competive and it has a very high skill ceiling.
CS:GO is based on the source engine, it gives you a lot of options for making game modes, maps and plug-ins.
At the moment I'm making a map and I find it very interesting to find the dynamic of a both playable and competitive map.