I have both.
If given the choice, and having to have one as a daily driver, I'd pick the Boxster.
I don't think there is anything my SC can do that the Boxster can't do better, with the exception of making that really cool noise that makes my girlfriend grin.
The SC has a cat bypass and sport muffler, and is lightened to about 2500ish. Even so, the Boxster seems just as quick, and handles better.
Getting A/C to work well in an SC or Carrera is going to add to the cost, you'll need a procooler and possibly underbody condenser depending on what the heat gets up to. Other than that a G50 Carrera would be a good daily driver, and an SC would be fine with a WEVO shifter and well adjusted clutch cable.
I drove my SC daily for almost two years, and it wasn't any big thing, but the Boxster is definately more comfortable, way better on gas, easier in traffic, etc. etc. etc.
Also, I have 80k on my Boxster and it runs great and doesn't leak or burn oil, I bought it with 69k in December. I've done a new top ($1700 for a glass window one, installed) and had some maintenance done when I drove it through a flooded street and it stalled out, but now that I have it back it runs great.