Reef tank is alot of effort, but certainly worth it. I have had loads of tanks over the years, but never a reef tank - which I have always wanted.
a Pico-Reef is a tough assignment though. You really need to have your marine know-how in place, even with the current systems in place. Small amount of water, changes happen MUCH faster. I had a 55gal saltwater tank that crashed over the course of 3 days, losing some pricey, -and even more importantly- very cool, entertaining fish. I had a Voltan Lion 6" long, a 7' panther grouper, a 20" snowflake eel, and a 5" Huma-Huma trigger, as well as some others... These guys were highly aggresive and carnivorous, and the eel and grouper were hand-feed-able.
ya want a cool fish? get an Archerfish, and do some target practice with it. They can extinguish a lit cigarette from 10' away...
Personally, I'd do both. Get a lesser laser - still fun, and you don't have to worry about calling aliens to invade earth, and a 10 gal. marine, and throw in some crabs and snails with some smaller herbivorous fish. You could do an anemone and clownfish if you test 2x daily.
As for size of tank, go as big as you can afford $/space. the bigger the tank, the slower the changes, and the more life you can enjoy in your tank.
enjoy both, not either.