I went through all this quite some time back... and what I came up with is an F28 f2.8...which that has led me to start to really want a 31mm.
In all that equivalency stuff a 28mm lens is roughly equivalent to the FOV of a 42mm lens on a FF camera... the 31mm would be equivalent to 46.5mm, and it allows f1.8 for speed.
I bought the 28mm and it is by far my most used lens now. I don't own the 31mm but rest assured LBA will get it for me. Just walking around with that focal length is awesome.
The DOF of a 50mm f1.8 at say 10 feet is .86 feet...the 31mm at f1.8 same distance is 2.27 feet. The 50mm will be less forgiving. At 5 feet of distance to subject the DOF is .55 feet with the 31mm.
As far as bokeh goes... that is all subjective. It depends on not only your distance to subject but your distance to the nearest objects behind your subject. It also is a function of what kind of background is chosen... I have taken a few shots where I was shooting stopped down but my other stuff was all in order therefore the 'bokeh' looked pretty nice at least to me.
It all just depends if you want to completely obliterate everything in the background or if you want to use the background to create an effect...
I can tell you this much though... my next lens purchase will be the 31mm. You can save yourself a lot of time by going ahead and forking out the money for one