I'd be tempted to get the 36 just because it's a cool old school snubby.
The 637 is about 4 or 5 ounces lighter than the 36 so it'd be a little easier to carry and if you intend to carry it then that's a factor worth considering. That said the 36 can be easily carried with the proper holster and belt. Plus it's a cool old school snubby.