The easiest and cheapest route is to take the airport's NORTH exit and then head west on TOLL 528 (Beachline Expressway) and then follow that route to I-4. There are two toll plazas, the first one is $1.00 and the second one just a few miles later is $.75. Both are staffed 24/7 if you need change. At the second one you have to technically "exit" the main road and pay at the booths on the ramp and then after paying proceed back onto the main road. Only those with a toll transponder remain on the main road. After the second toll plaza, the road remains signed as TOLL 528 but there is actually free movement all the way to I-4.
For Universal, when you get to I-4 head in the direction of Orlando. The signs will say I-4 eastbound but directionally the road actually heads north. At the second exit, EXIT#74B and signed "International Drive", turn left at the top of the exit ramp and you go directly into Universal. Access to the hotels and the theme park garages are clearly marked.
For Disney, when you get to I-4 head in the direction of Tampa. The signs will say I-4 westbound but directionally the road actually heads south and then curves southwest. Once on I-4, the first 5 exits are all Disney World exits.
BobK/Orlando