Aruba is a second tier site. But great for wrecks: the Antilla, the largest in the Caribbean but falling apart, a couple of airplanes, the Jane C, a small freighter sitting upright in 90 feet. The west end off Palm Beach has low and scattered heads, but a good selection of fish around the Pedernales, a blown-apart wreck. Saw three very large Blue Parrots there. Also good for a night dive. A slipper lobster lives there. Best coral sites are off the south coast. Sheet, fingers, and large, connected heads with lots of critters. Only occasional reef and nurse sharks.
I've used Unique (bought Pelican operation), Red Sails (cattle boats) both on Palm Beach, SEAruba, and JADS south and east. My choice is SEAruba. It is a Dutch operation located just west of the airport and a shorter boat ride to the south sites. JADS is a new shop near Baby Beach on the east tip. Also good, with a new boat due in '09. Both shops will pick up and return to resorts. Both are also open to your choice of sites.
Harbor reef, Mikes, Fingers are good.