I have handled M3's and M3T's and I personally have a Mag 2C with 3 X CR123's. I also had a Streamlight TL-3 incandesant light that I sold a few months ago.
What are you primarily using the light for?
MY Mag 2C goes through KPR112's (from Radio shack) like its cool. I ran out (after buying 5 and flashing them all, they are rated at 7.2v) now I run a 6 cell Magnum star in it which is rated at 9 volts.
I bought my Mag 2C a while back for like $12. Then I recieved a 3 X CR123 holder for the batteries made out of PVC pipe and big rubber bands to keep the batteries secure while in the flashlight, then the bulbs from radio shack are like $1.50 each, and then I bought a metal mag reflector for $25, and a UCL for $7. So my total cost is $45.50. Sure you can get by for $13.50-$15, but with the hgiher heat of an overdriven bulb and wanting to have a nicer beam (op'd metal reclector) it is still under $50.
The Streamlight TL-3 incandesant cost me $60. The Surefires go for $252 for the M3 and $308 for the M3T.
"Sometimes cost doesn't matter."
Cost doesn't really matter when your life depends on a flashlight. Sure the Surefire's are expensive but special forces guys in afghanistan, a SWAT team, or other LEO/military members rely on a durable light and some of them go with Surefire. That has to mean something.
Size is also another issue, the Surefire's and TL-3 are much smaller compared to the Mag 2C.
I don't have a M3 or TL-3 on hand, but here is my M6 and Tigerlight next to a 2C. Sure it has a skinnier body but gosh its long.
http://myspace-040.vo.llnwd.net/00151/04/06/151526040_l.jpg
I had my Mag 2C and SF M6 in my back pack when I go out because I was too lazy to remove them after a few long and sometimes trips (Spec Ops THE pack which I stuff a lot of stuff into and just keep in the turnk of my car for those just in case situations), the M6 still worked when I removed it, the MAg 2C did not. It is fragile because the bulb is being over driven (KPR112.) The Mag 2C now has a Magnum star bulb but then again Mag's weren't made to endure being fired close to a high caliber rifles.
So IMHO, The SF M3 kicks the Mag 2C rear end in every aspect but throw and cost.