I've driven to Orlando from Miami probably over a 1,000 times so I know every route possible.Easiest best route is the Turnpike the whole way but it will cost you about $14 with Sunpass since it gives you a discount,if you pay cash it'll be more,in the $17-$18 range.One thing to avoid is 95 from West Palm Beach south anytime around rush hour,basically 7am-10am or 3pm to 7pm,if you're going to drive around this area during these hours do the turnpike.
If you want to save a little on tolls but still take the Turnpike which is a more direct route to Orlando,take 95 to Ft.Pierce(exit 129 in 95 and 152 in the turnpike)get off 95 and switch over to the turnpike which is only one mile from 95 at this exit,you'll only pay $6.50 with sunpass or $8 in cash.
You could take 95 all the way to 192 (exit 180) which 192 is the road which travels through Kissimmee and St.Cloud directly to Disney,192 from 95 to St Cloud is very rural but really not a bad drive and you will not have tolls,but will probably take a little longer.
You could also just keep going past the 192 exit and reach the 528 expressway (I believer it's exit 205)called the Beachline or the Beeline,this way you avoid going through a rural area,avoid the red lights in Kissimmee and St Cloud and you will only have three inexpensive tolls totaling about $3-$4.This route however is probably the one where you will travel more miles since you're driving all the way straight and then making a left turn,unlike the Turnpike where you're just cutting to go directly to Orlando.
If you want to take a totally rural route the whole way take US 27 that will take you through the small little towns around lake Okeechobee and up through Sebring and Winter Haven.I'm taking this route to go to Legoland this week in Winter Haven.I would however suggest not going this route as you will have to slow down through the towns and the towns around the lake are not the nicest,once you get north of them the other ones like Sebring are nicer,no tolls though.When you hit I-4 from US 27 go east towards Orlando and Disney will be about 10 minutes away.
As far as time goes,there have been times I've gotten from Miami to Kissimmee via the turnpike without traffic in 3 hours 15 minutes,from Ft.Lauderdale that would be around 2 hours and 45 minutes,any of these other routes you're probably looking at 3.5-4 hours minimum without traffic and the US 27 route probably 4-4.5 hours so timewise stick with the turnpike.