What is the best side by side double barreled shotgun which is steel shot proofed?

It depends on what you means by "best."

If you want a good solid working SxS that can handel steel I think there are two good choices:
(1) Fabarms Gold Lion. Good price (arround 1,400), with choke tubes, double triggers, etc. Its a heavy gun though, so its good for clays or waterfowl, but I would not like to carry it far. Also not the most attractive gun...

(2) Beretta 470. Lighter gun, more "game gun" configuration. More expensive arround $2,000. But its got a single trigger, which for me was a problem, but might not be for others.

I went for the Fabarms, but I think the Beretta looks nicer and is probably better made.

Just my thoughts!

"Parker Reproductions" "Steel Shot Special"...Arguably the best ever SxS specially designed for Steel Shot....Good luck finding one!

These guns were regulated for high-speed SS loads and according to Michael McIntosh shoot better than anything he has ever shot....He ain't the only one thinking this way!

Jeff