Having been to both I can help you out a little..
Cypress Gardens is about 30 mins from WDW, so its closer then Busch but it is a MUCH smaller park, I was there last January so I am sure some changes have been made, currently they have several small family roller coasters (like those found in a normal amusement park) I would recommend checking out
www.RCDB.com and type in Cypress Gardens and it will list the different roller coasters and pictures to give you a better idea. They also have several very fun smaller flat rides. The highlight to Cypress Gardens is its gardens which are absolutly beautiful, but kids might not see the value in wandering gardens for an hour or two. They also have a nice ski show, not as good as it once was but still good.
Busch Gardens Tampa is about an hour to an hour and a half away from WDW (might be further my memory is not so good on these things) and it is a HUGE park, I personally like it better then Animal Kingdom, AK borrows ideas from Busch in many ways. First of all its themed around Africa as a continent each section like Nairobi, Egypt, etc carries its theme fairly well. The animal attractions are well layed out, very interesting, and if you kids love animals this is the best place out of the two. Plus the park has several VERY good roller coasters, Kumba, Montu and Gwazi are probably to big and to wild for the 6 year old (plus the height requirement is 52" I believe) but the park does also have a wonderful ski ride, train ride, safari ride (like Kilimajaro Safaris but its called Rhino Rally at Busch) a few good smaller rides, and Scorpion is a good starter looper steel coaster, not to big, but a lot of fun. The park is HUGE though, so get a map before hand and decide what you want to see because its impossible to see the whole park in one day, but worth the journey.
Both parks are nice, so you really can't go wrong, but if you are looking for a good 1st experience away from Disney I would recommend Busch.
Jennifer
I have two question!
1) We are family of 5, 2 parents and 3 kids 6-6-9 yo. Wich park is better CG or BG???
2) How far are does park from Disney/Orlando area??
Because we might arrive a day early, and wanted to do something we've never done with the kids! Would love to do Universal but my kids are too small for that
Thanks for helping me!!