If it's not going to be that much of a difference in time to get to the parks then I would base my decision on how much you like coasters and what month you plan to visit,Busch Gardens being the park with the most coasters in Florida would be my decision if you do like the thrill rides and are not going at a busy time.Sea World is building a new coaster but they're still behind in the thrill rides category but it has more shows which are spaced out throughout the day making them hard to do in 1/2 a day.I would also consider what date you will be visiting,if it's not a busy day I would probably go with Busch Gardens simply because on days with light crowds the waits are not that bad for the rides,you'd be amazed how many you can ride in just a couple of hours.At Sea World on the other hand the lines can be a bit longer even on days with low crowds and more importantly if you were planning to do the shows it would be hard to try to fit them in in just a half day visit.Sea World is always going to require pretty much a full day in my book if you want to do several shows and the rides.BG is more rides based with Sea World being more show based so you would probably get a lot done if the lines are short at BG.Being in Tampa the lines will never be as long as the Orlando parks,you will be going on a Saturday so you will get weekend crowds that are bigger than a Tuesday crowd.I would say I would base my decision on what date you're going,if it's a low crowd month go with BG,if not then SW and try to do the most you can,there's less rides to do but you won't get most of the shows and attractions done in 1/2 a day.Based on your kids age the coasters may not be what you plan to do at the park,in that instance also go with SW as both parks have a section for rides for kids.