I've never owned an inflatable, but I can tell you that my 9 year old son and I have really enjoyed our 12 foot tin boat. I power it with either an electric motor or an old 4.5 Merc, and it does really well on lakes. The boy and I have more than adequate room, and we can accommodate one other person if need be. I have it set up with rod holders, a boat seat for me, a portable fish finder, launching wheels, and even a downrigger, so its really functional. The other advantage is that I can travel with it on top of my SUV, and consequently we've been able to explore some more remote lakes that you might have trouble getting a trailer into.
I'm sure there are other workable options, and one day I'd like to get a bigger boat, but I believe we'll enjoy our little tinny for many years.