So what have you found to be the best all around dinghy?

You might want to consider a 04 to 07 Saturn Vue 6 cyl. There are tons of them being towed. I've had no problems whatsoever with mine and now that Saturn Corp. has died they can be had fairly cheaply. Don't be concerned with parts availability. With the Honda powertrain they are very peppy and fun to drive. Plenty of room for the dog.