I'd have to say the most rugged is the stainless steel Smith 5906.
This^ and the 4506. I have not submitted mine through torturous tests but I can't imagine it failing. I know everything breaks eventually but I just cant picture it. I've seen glocks cracked and broken, XDMs blown up, I've even seen Redhawks blown to shreds(there were extenuating circumstances to this one but the point stands), but I've never heard of or seen pictures of the 3rd gen smith and wesson autos failing in any catastrophic way.