Which would make a better daily commuter (I need the HP, so pls don't recommend a Corolla)? Which would be less expensive over the next 6-8 years taking into account insurance, parts, maintenance, tires, etc.

that's an easy one, SC400. Possibly has one of the strongest and most reliable V8's toyota has ever produced. A little more $ to maintain but you wont be maintaining as often as the mustang. ;). Has a little less power than the mustang (off the line)but that can easily be changed by opening up the exhaust and induction as well as a torque convertor. On the highway, the mustang can't touch the sc. With high flow exhaust the sc sounds like po'ed camaro. Insurance will be just a hair less than the stang. If you keep the stock wheels, tires are less expensive but thats up to you. Has a better stock stereo.lol What else can i add? If ur after power and you'll be using it daily, the mustang will be done in 4 years, especially if ur putting miles on it. i have a 16 year old sc with 137k miles on it and it can still hang with z28's, stangs, etc. Buy an SC