During the past 4 years we have vacationed in St Martin 4 times & Aruba 4 times.
They are both AWESOME! Both have beautiful beaches, fantastic restaurants & great resorts. We think our dollars go a bit farther in St Martin, than Aruba. I love both places & plan to continue to visit both each year. However, if I was forced to choose only one, it would be St Martin. This is where we stay in St Martin:
http://www.esmeralda-resort.com/
This is the beach, beach bar/restaurant connected to Esmeralda:
http://www.cocobeachsxm.com/
These are some of our St Martin pics:
http://picasaweb.google.com/flfreedomfighter/StMartin
These are our Aruba pics:
http://www.dropshots.com/1marksman
Hope this info is helpful.