You will definately be better off with the 44 mag. I have a Ruger SB 44 mag and I love it. I've killed a couple of does with it.

The 357 is big enough to kill deer, but you'll be pretty limited on your effective range, especially with the shorter barrel.

And about the sights, the fiber optics will be an advantage. It's much faster and easier to focus on a target with them.

Good luck,