Functionality, you cannot go wrong with either.
To me, the Rugers look a bit frumpy, but remember, beauty is in the eye of the beholder.
I do not have a 357 Magnum GP100, but I do have a 327 Fed Mag and 44 Special GP100's. I have a few S&W 586 and 686 revolvers chambered in 357 Magnum. Also, Model 69 (44 Magnum L-frame).
The grip frames are a bit different between the two. I find the difference fine as I like rubber grips but many folks like wood grips and there are lots of different models of grips out there.
Barrel length is another variable. I'm not fond of 3" barrels in 357 Magnum guns but I do have a couple. 4"-4.25" is good, longer up to 6" is better in my opinion. I have an 8-3/8" barrel 686 which is quite accurate but the long barrel length makes it difficult to carry.
(P.S. Because of the 8-3/8" 686, I've gone a 8-3/8" S&W revolver quest and have a few with several different cartridges, 8 at last count, Model 29, Model 25, Model 57, Model 27, Model 14, Model 686 Model 48 and Model 17. They are fun to shoot but not real convenient to use and carry.)
If you can get an opportunity to shoot both, borrowing a friends or a rental at a gun range, that may help with your decision.
Good luck.