Elmer,
The ketch is regarded as being a lttle more balanced than the sloop as the main mast is in the same position. Sloops can be a little cheaper and supposedly harder to sell but that may mean a better bargain for a shopper.
For Med cruising the smaller size can be a big advantage but for blue water cruising I would suggest you keep an open mind as the Super Maramus are designed to be very easily sailed for their size by a couple There are more Super Maramus around and it may be easier to find a good one at the right price. The galley is much bigger on the SM. For permanent live aboard this may be handy to you.
Looking at 20 year old boats I would suggest the vessel's condition is more important than the exact model. The similarities of build quality, centre cockpit security, machinery layout, design details, non-cored hull construction, rigid lifelines etc etc are common.
John, Maramu #91 Popeye