Im a mazda guy at heart but im gonna have to go and say id put my money on the sti. Unless you want something more refined and luxury oriented, then id tip my hat to the ms6. Otherwise its all sti. Im a subaru technician and i must say that the STI is a very well built performance car. The sti a car we see the least, and it has the least amount of failures. The car is damn near bulletproof. Clutch issues, tranny issues, turbo failures, the typical things you may hear about other cars are very rare on sti. The sti is a great choice for a stock platform or a buildable platform. No im saying this bc ima subie tech, cuz I loooooooooooooooove my miata, but in comparison between the ms6 and sti, sti ALL day. But dont take that as the ms6 being junk. Its still a great car. My main issue with the ms6 is its weight, its a bit heavy. But for what it is its still a great package at a bargain price.