I investigated taking capeair a two years ago, but one-way off-peak was about $110 each -- That's a nice meal a Chesters!
The fast ferry runs in the summer and is about two hours - which by time you get to the airport, etc... It is also about the driving time (which as BVH points out is boring!)
My vote is that if an hour or so isn't of the essence and the weather is nice, get a jump on your tan and fast ferry it!