Historically, VSC has always been the fastest of all the offices. You can search back years and still find disparity. With the fee increase last July, as well as the split of States to each office, one would assume things would even out but obviously, that's not happening.
I agree with Grandoner comments in regards to a lawyer. Unless your circumstances are extreme, you wont need one.
As others have stated, the K1 visa is valid for 6 months from the day it's issued. Then you have 90 days to marry once you've entered. You must keep in mind that it is a 1 time only entry, though.

Whatever you choose to do... best of luck!