Given that the fan itself is fairly large, I don't see much to be gained from changing from SOIC to the smaller package, but I can see disadvantages;

a) A lot more people here would be capable of building a kit with the SOIC.
b) SOIC is a very standard package in pcb editors, including freeware editors (eg Eagle). You might have to create the pin out for the other package, (effort, chance of foul up.)
c) You'll have a better chance of good results from cheap boardhouses with the larger pitch.