Well, a quick look at the Universal Park Hours should quickly make up your mind for you!
On Thru. April 26th, both parks are open until 8pm. However, on Friday, both parks close at 6pm! So, Thru. would be your best bet!
Keep in mind, Universal has TWO Disney size parks both with amazing rides and shows. Unless you want to skip out on a lot of things at Universal, I suggest skipping Sea World and doing Universal both days and save Sea World for another time.
You could always wait to purchase your Sea World tickets and decide when you are there. Since you will hopefully do Universal first (because of the park hours), you can decide if you want to come back on Friday to do things you had to skip over, or if the few rides and shows at Sea World is worth the trip.
I would really look at the park maps and rides at both Universal and Sea World. If Sea World sounds like it has a lot of stuff you want to do (a lot of shows and only a few rides) then you will want to do it. However, if there are a lot of things you want to do at both Universal parks, you might want to wait. Like I said, these are both big theme parks with lots of rides and show to do and unless you are racing around the parks with the express passes, you can not do everything in one day. You can easily spend a few hours in the HP area alone.
