I got my full OW cert with Red Sail. It started out as the 'discover scuba' through the hotel (from Red Sail), and I was so fascinated that I spent the rest of my vacation in the classrooms. I really enjoyed Red Sail. My instructor was Anthony, a current police officer down there who does the scuba thing on the side, and he was an absolute class act! Very thorough, very patient, and very good. It was only me and another couple who were getting certified then, so the individual attention was great. The dives I did afterwards with them were 'cattle' boats, which I've come to dislike, but my instruction with Anthony was top notch! I can't reccomend him enough!
Either way, the diving in Aruba was awesome - you're gonna have an excellent trip!!! As ScubaFrog mentioned, you must see the Atilla! That's an incredible sunken ship!! Very cool site, especially for a new diver! Bring LOTS of high SPF sunscreen though, the sun is VERY strong down there!! I normally don't wear sunscreen since my Italian skin doesn't burn easy, but by the 3rd day I was just about lathering myself in 55-65spf sunscreen made for babies! Luckily Aruba's #1 export is Aloe-Vera! haha!!