I guess I'm bucking the trend here but for only one pistol I'd have to pick my G20/21L. As roughly the size of a 1911, it actually conceals better than a wheelgun because of it's thinner profile. Also, loaded with 17+1 rds of 165grn 10mm and the range only magwell removed, it weighs less than a 6" S&W 686 loaded with only 6 rds of 158grn ammo.
I reload for all my weapons so I can produce both light and heavy hitting 45acps and 10mm. As far as the 10mm's power vs a .357mag is concerned, check out Double Tap's performance of their hot .357mag and hot 10mm loads out of a 6" barrel. You'll note that their 10mm loads equal the performance of the 357 when both are shot from a 6" barrel.
In addition, the recoil produced by a 357mag in a wheelgun is considerable for many people while the recoil in my Glock shooting my hottest 10mm (165grn @1,503fps) is much, much lower. My 5'0" tall, 105lb wife can shoot a mag full of my hot loads in my Glock and control it well. However, when she shoots my 357s in my wheelgun, she'll shoot only one round and she's ready to turn it back over to me.
Yep, for mouse fart >600fps to fire breathing <1,500fps performance with a 165grn bullet, I'll take my Glock 20/21L over my 357mag SAA every time.