In my ignorance (and it is ignorance) and given the choices, I would give the nod to the Galaxy S:

Based on what I've read (a lot of stuff):
1) SAMOLED screen quality is quite a nice feature
2) The Sound quality is supposed to be incredible (unloaded -- on par with iPhone4)
3) Touchwiz is supposed to be very light compared to a deeply integrated Sense
4) Battery life is supposed to be better on the Galaxy S
5) The Galaxy S is the better performer
6) The Galaxy S camera is very good, and has great low-light performance (even lacking a flash)
7) The Galaxy S is more compact and thinner and lighter (though the screen is smaller)
8) Reviews of the Galaxy S are resoundingly positive