Most people go to PR in the winter for the North swells that come down from the east coast. The wave season is Nov. to March. The main destination is the Rincon area on the other side of PR. Having said that, it is possible to get waves any time of year on one of the coasts of PR. Your best bet will most likely be along the east side of the island between San Juan and Rincon. I would guess that you will find some ridable waves, just don't expect to be surfing large ground swell in the best of conditions as you might find in the winter on the NW facing beaches.
PR can defiinitely hit in April. It not quite as reliable as februrary or march. But on the north coast there is generally a pretty consistent trade swell. I've personally never surfed over by San Juan, but there are some very good breaks.
Rincon is on the west side and a long ride from San Juan. If the swell is right it's worth the ride, but I wouldn't bet on it in April. Its a bit difficult to surf in the San Juan area if you're not familiar with it. Rent a car and go west of SJ towards Dorado, Manati, and Isabela. Lots of spots that will pick up swell through the spring and be sheltered from the trades. The north is pretty consistent and can get real good. Bring some reef booties if you're not experienced with surfing reefs. Or go east towards Luquillo. The east side picks up trade swell all year long, but it's rarely offshore. Go to La Selva surf shop in Luquillo and they should help you find a good spot. You can hit Luquillo in the morning and visit the rainforest (El Yunque) in the afternoon. Just remember to be respectful down there. Outside of Rincon there is some animosity towards gringos and there are plenty of gringos that go down there acting like arses to make it worse for those of us who don't.
How did this trip pan out for you? I am possibly going on a trip in April.
Killa I went in April for my B day two years ago and it was a great success. Going again this April. I'm 3 for 3 on my trips to Rincon, two of them in October, one in April, so this will be my 2nd April trip and 4th total in the last 2 years. I wouldn't go to San Juan though, it's further than people think. When on vaca the last thing I want to do is road trip it like I do back home all the time. My wife and I decided we would make the trip from Rincon to San Juan one day and we ended up stopping in Barceloneta, at that nice Outlet Mall they have. We turned around and went back to Rincon after that. F that drive. HAHA