I'll actually be there around both of those dates. The Feb. date is around our Mardi Gras holidays (and is a rescheduled trip from my Labor Day trip Isaac ruined!). My April trip is April 20-26, which is our spring break.
I've gone around these same times for years. Feb. weather is cooler, but I find the crowds less in April.
If I had to pick between the two, I'd pick April because it should be less crowded. Mardi Gras increases the crowds and then with Presidents week following right on the hills of Mardi Gras, I think it's going to be alot more crowded in Feb. Mardi Gras day is Feb. 12. Alot of people from here will be there the entire week from Feb. 9-16. Presidents week is the very next week so as the Mardi Gras crowds are leaving, Presidents crowds will be arriving. Although it will be hotter in April, Flower and Garden will be going on at Epcot and it's really beautiful there! And like I said, the crowds shouldn't be as bad as your Feb. dates.