It's very hard for guys to pick the ring. They get overwelmed easily and they have different tastes with women.

If you try to avoid the trouble that you might have to change some parts of the ring, I suggest you go with gg. The alternative way of suprising part can be: gg propose to you with a fake ring, like a plastic one or paper one. Then you guys can go pick the real expensive one together.

If you don't mind that you might get a ring that you don't like 100% and would like to do all the changes after, let gg pick by himself.