Speaking from experience, The Mach 3 is much better.
I used the Schick Xtreme 3 razor once and hated it. It feels so cheap and ended up getting 2 shaves from this razor.
I usually buy the Mach 3 from the Local Target store.
I though I would try the Mach 3 being advertised from a guy at Fle*bay.
He sells what is called "Cryo'd" which is suppose to be a tempering process.
His list reads...
"Cryo'd Gillette Mach 3"
Being the skeptic that I am, I figured since these cost about the same as the ones I get at Target, I'd give it a try.
Well, In 2 months, I'm about to begin using my second blade.
Where as, I normally get about 3-4 shaves from a normal Mach 3 blade, I got over 8-9 and the wife uses it in the shower too.
A definite Deal!