I think you need a third option.
I personally don't think the 15" MBP is too big based on my experience with the previous model.
However, the new MBP does seem a little heavier and bigger making it less portable.
Ultimately, I think the MBP is portable if you don't carry it around all day. But if you're constantly on the go then no.
if it's just from the car to office, car to home, its fine.
17" definitely not portable.