Steel is a bit heavier to carry but it is a whole lot tougher than aluminum. I personally would not care to mate steel to aluminum; I just wouldn't trust the aluminum not to deform.

I once had inexpensive aluminum see through mounts on a Remington 742. I hated the rifle for years. Last year I put Leupold steel mounts and rings on it and it does make a difference. The aluminum mounts wouldn't hold the screws tight over time, even with Loctite. This still isn't my favorite rifle, but the scope mounts are no longer a point of irritation for me.

You might be ok with the aluminum Weaver-type mounts, but I personally will use steel every time.

Just my 2 cents worth. Good Luck!