You're comparing oranges and apples. The M3 costs twice as much as the Sti here in Australia. In terms of Bang for buck, the Sti is the way to go. Also, the MY06 Sti now has that ugly front end (which is not in that picture), along with a 2.5ltr motor, the rest is the same as the MY05 sti.
The 06 makes more power than the 05 on less boost, but there might be some questions about the strength of internals. It has a 6 speed gearbox which as far as I know is fairly strong when compared to the 5 speed in the wrx, meaning you can give it hell off the line more often
If money is an issue, and you want a car that's focused on performance but is comfortable and refined enough as a daily driver, then go the Sti.
Don't forget with Subaru's all wheel drive, the Suby's performance in wet weather won't be far off its performance in dry weather. An sti with a few grand in mods will run 12's all day, it has that sexy boxer burble, and uh, I'm a little biased. Having said that I'd look at an evo 9 if you can deal with the cheap interior
Of course if this is about gt4 then I've just wasted a whole minute!