1. Car rental: This could be best option available it will several hours that you might waste travelling from to and from the airport to Unviersal. This works best if you plan to visit other theme parks like Disney, Seaworld. Only problem is parking fees that you end up paying, but still it would be worth as you can spend the extra hours that you save inside the park.
2. Taxi: Its good option saves you parking charges, but it might turn out expensive. You will get taxi from Airport and also there is taxi stand when you get of Universal. So its really convinient if you dont want to go for Car rental.
http://www.mearstransportation.com/global/orlando/
http://www.cityyellowcabs.com/
3. Bus: Good economy option no need to worry about parking charges, but be ready to add 1-3 hours to your trip to and from universal. Orlando is server by LYNX bus service which has good frequency. Living in Orlando without a car I have been using this option for all my travel to the theme parks and it works the best for me. Following are buses from Airport to Orlando, you need to change the bus
1. Catch 42 or 111 from Airport and get down at FLORIDA MALL(around 20-30 mins)
2. From Florida Mall catch 37 (Pine Hills) it will drop you at Universal gate(around 30-40 mins)
You can get a ticket for $2 in bus (keep the exact change, drivers won't give you change) for a trip to Universal ask for Transfer which works for 90 mins.Other Option is to take a day pass in the bus for $4.5 (keep the exact change, drivers won't give you change) and you can use it for the whole day to travel all over orlando. Check for bus routes and schedules at below LYNX site
http://www.golynx.com/
Both parks are awesome, make sure you give enough time atleast(1.5 days each park) 3 days for Universal to have a real fun vaccatioin. I have a annual pass and we enjoy the park at our leisure we took 7 days to cover all two parks. Some times wait for major attractions can be more than 90 to 120 mins