I've got Patagonia Swiftcurrent Expeditions and Simms G3s. Both are very nice, but the G3s fit me a little better which is a bigger deal than I thought it would be. Aside form fit, the biggest difference is the weight of the materials I think. The SCs are way heavier and maybe less breathable than my G3s. But the SCs also seem to be more thorn resistant - my G3s are a little old but I am constantly putting holes in them. So I use the SCs in winter and the G3s in the summer and fall. Also, the SCs aren't the zippered model so getting them on and off without buckles on the suspenders (why Patagonia, why) isn't as easy as the G3s.
Regarding warranties, both companies have been good to me, but Patagonia probably wins by a nose in my experience. They really don't ask any questions and don't charge you a cent. They even sent me a shipping label for a repair.
Ultimately when I need another pair I'll probably go Simms because of the fit and the fact that my local shop carries them.
Edit: I just looked at the OP again and realized this was about pants not waders. Oh well.