We've been able to dive both Aruba and Bonaire; for honeymoon fun, I'd pick Aruba. The beaches are far more spectacular in Aruba. Calm at Eagle Beach and Malmok -- beautiful for snorkeling.
Rent a car for one day and drive out to Baby Beach -- good way to give yourself an island tour. Go snorkeling around Palm (de Palm?) Island, but don't waste money to get to the island.
RIU is nice -- haven't stayed there, saw it being built -- looks like a super place for a honeymoon; just walked past. You will be in a good location for casinos and fun restaurants. The casinos by RIU have nice bands in the casino area sometimes. Try the ribs at Smokey Joe's -- fabulous. One night is all you can eat (inexpensive, even without). Try also the Salt and Pepper restaurant.
Diving -- we used USA (I think it stands for United Sports - Aruba). They just bought two operations, so they will be the largest on the island on that side. You set up your gear; they put the tanks in the boat. Dive masters accompany you; don't do a lot to show you specific marine life, unless you ask up front. People are nice; the shuttle driver from hotel to USA is very nice, cooperative, dependable. I think Lucia --at front desk of USA -- works out your overall discount only after you have done your dives (thereby giving you the best deal).
Viz was not that great, but wrecks (Perdenales, Jane C, Antilla -- the USA dive masters give nice history detail) are nice. Aruba has a lot of wind. B/c of that, the wind whips sand even into the shallower depths.
Horseback riding is far -- bring hat and sunscreen.