Steel w/o a doubt. Gun is so small, weight should not be a factor.
For shooting weight will reduce recoil. Gives you more control and accuracy. Youve got a short barrel, and will be shooting at a close range, you want that slug to go where you point the gun.
BTW: get some soft Hogue finger groove grips. Every handgun I own wears them, and the are very comfortable no matter the cartridge, but really help with stuff that has more umph.
Behold a pale horse, and the man that sat on him was Death, and Hell followed with him