UNIVERSAL ORLANDO,hands down should be your first choice.
On the other hand,at night many flock to Old Town,which also is a favourite of mine in Kissimmee. The Congo River Mini-Golf and the Pirates Mini-Golf are also enjoyable. International Drive is full of stuff to do,especially the Magical Midway,which houses a space shot free-fall ride,a couple of go-kart tracks,an arcade,laser tag,and small carnival rides.
Shopping spots include I-Drive,The Florida Mall,and The Mall at Millenia.