While both the Maldives and Phuket have their respective strong points (I've dived both), as you are a novice diver, have only a long weekend and cost does not seem to be an object, I'd recommend the Maldives.
More specifically, you may want to consider the Ellaidhoo Resort, which has a very nice housereef. I've never dived at this specific resort, but according to Tim Godfrey's excellent book, "Dive Maldives", he claims that "of all the resorts in the Maldives, Ellaidhoo has one of the best and most convenient housereef dives." He goes on to state that "Ellaidhoo divers can dive the housereef whenever they like and rarely complain of being bored." He rates it a Beginners site, if conditions are suitable. His book lists fish life for the reef as very good and coral growth excellent.
If you choose not to dive, snorkelling on the housereef is also an option, since you will have your mask and fins with you.
Your planned travel period of April falls within the transition period between Monsoons in the Maldives. In April, calm, windless days are more likely to be experienced than at any other time of the year.
If I'm not mistaken, the dive operation there has been managed by a reputable European operator for at least a decade.
It sounds like a very good place for a novice diver to spend a long weekend!
You may want to do an internet search for "Ellaidhoo" for further resort/diving details. I have no affiliation with them.
While Phuket has a lot to offer, IMHO diving the better sites around Phuket is more suitable for divers with a little more experience than you currently have. I was there in January doing day-trips and there were many novices who were seasick from the boat rides and who were obviously struggling with some of the conditions at the better sites.
Whichever you choose, enjoy !