Wilderness is good for cardio and general xc speed work. It's flat and twisty with lots of roots. It's a good ride, I do it a couple of times a month, but it's not worth renting a bike for.
My recommendation would be to hit up Alafia and Boyette. Alafia is smaller and easier to find your way around. The trails are on average a bit more gnar than Boyette and the expert stuff is more challenging. Boyette is IMO a more fun park though. The trails flow a little better and you get bounded around less. More elevation change as well. Ridgeline is probably the most interesting of all the local trails. Definitely worth the time it takes to pedal out to the back of the park. Its pretty easy to get lost at Boyette though. Be sure to print out the map as there are frequently none at the kiosk.