Why should I choose 36 or 32 spokes (or another number)?
Lower spoke numbers are primarily of interest to weight weenies (though for a given price, a lower spoke wheel will probably use a heavier rim offsetting the spoke reduction weight savings). 

As usual, Sheldon is some good reading. There is also a whole book on how to build wheels well and design decisions, by Jobst Brandt, called "The Bicycle Wheel".

What matters for most people is using a good amount of spokes, good spokes, a good rim and hub, and putting them together well (and how they're put together) - pretty much any wheel is going to be bad if the wheelbuilder messes up/sucks. 

Heavier riders often should go with a higher spoke number than a lower spoke number and tougher rims+spokes. According to Sheldon, it used to be that you'd run 36 front, 36 back then we started dropping. On a commuter, I'd emphasize durability, so I'd probably go with the more spoke option.

The best thing to do is talk to a good wheel builder and assess your individual needs. If you got to the point where rim wear was what made you replace the rim, chances are you're fine with whatever you had. If you're replacing the rim, make sure to use new spokes and make sure the hub is in good condition.