We have always loved St Martin since first going there in 1982 0n our honeymoon and have been back 8 times since then. Going again end of April 2016 with friends to their timeshare. It has changed a lot since 1982 some good some not so good.
Have been to Aruba twice in the past years and stayed in different villas in the Arashi beach area. We love Aruba for its beaches, numerous gambling spots, shopping and restaurants. We also feel safer in Aruba and that is one of the things that has changed in SXM unfortunately over the years. Aruba has excellent beaches, the 4 wheel drive tours and various water sport activities but not a lot else. That's OK for us because we just enjoy relaxing but that might not appeal to all.
Car rental and driving is very easy in Aruba. The roads are good and you drive on the right hand side of the road. Some of the signage to areas on southern end where Baby Beach is (very nice beach calm water) could be better. We haven't done condos but there is a number of Marriots and I believe they have time share units. Last time we were there they were just finishing building a huge food store in the Palm Beach area where most the high rise hotels are.
Been to Barbados, Antigua and St Croix YEARS ago and enjoyed them but then started going to SXM and never went back.