DME is great; but if you can possibly do all carry-ons, do it - for multiple reasons. If DME isn't an option (non-Disney resort/hotel) then go with MEARS, which is the local heavyweight in vans/busses to/from MCO.
I too am interested in seeing more reviews from people here who used the services.
Also I have a question - I see that the towncar is geared for up to 4 people (at least for QST). If you also had a toddler in addition to the 4 adults, would you need to upgrade to a larger vehicle?