I'm a big fan of the 35mm F/2 IS. I put mine on my 5D3 just now and compared the autofocus speed to my 24-105 F/4 Mark I which was set at 35mm.
From MFD to infinity takes the 24-105 a bit over 1 second. The 35 F/2 takes a bit less than one second. Those are rough estimates of course. Both are more than fast enough for my needs, but I'm not a sports photographer.
If you can afford the 35 L II, go for it, but the F/2 IS is a very nice lens too.