Have owned a P6 and assorted Smiths. No longer own a P6, but do have other SIGs. Nothing wrong with the P6 per se but it's a bit bulky for a single stack nine, good quality spare mags can be hard to find and expensive, and hollow points can be an issue. It's not all that much smaller than a 228 (which I do own and was the biggest reason I ditched the P6). At their original price the P6's were a bargain, present prices seem to be in the upper 300 low 400 range and at that price point there are lots of other choices. While I didn't hate the P6, I never really warmed to it either.
I really like Smith nines and have had excellent luck with them. The 5900 series is not exactly petite; if CCW is high on your list you may want to check out the 6900 series or even the single stack 3900's. Mags and leather are plentiful and generally fair priced.
Accuracy, reliability, general overall quality I rate as equal. Price is probably about a wash in the present market. Availibility definitely favors the Smith. Lots of them still around, P6's have dried up in recent months. I voted Smith.
If possible try both. If one fits better than the other go with that one. Nothing wrong with either.