For me, it depends on where we're coming from (including whether we take the Auto Train), where we're headed in Florida, and whether we stop to visit our friend who lives southwest of Jacksonville at Lake Asbury.
If we take the Auto Train, which drops you in Sanford, we use either of the tolled beltways around Orlando. I've become partial to the western side (FL-429).
If we drive the whole way and we aren't going to stop near Jacksonville, I sometimes head across to I-75 further north. A few years ago Mapmikey suggested using Georgia's Fall Line Expressway from Augusta to Macon. It was a good route (and it is substantially more complete now than it was then), so I've been thinking about going that way again. We connect to Augusta via either I-77 or I-95 to I-20.
If we do stop near Jacksonville, we use the new FL-23 toll road down to Lake Asbury and then I'll usually use some combination of FL-16 and FL-21 to US-301. Then it's just a case of how close I'm willing to get to Ocala before getting back on the Interstate.
A couple of years ago, I used US-17 south from Green Cove Springs to DeLand, then cut southwest on FL-44 down to near the end of FL-429. That route was good as far as Palatka. It was fairly slow south of there and I doubt I'll go that way again. From Palatka, FL-100 and US-1 across to I-95 are a good way to go and I would do that again.
For our upcoming trip south, which will include a stop near Jacksonville, I am considering using FL-19 from Palatka to the Mount Dora area, as Max Rockatansky suggested in another thread, but I'm undecided because it's a long stretch on two-lane roads and I'm not sure whether my wife will stand for it. We're heading to Weston, so I may cut west via US-301 to I-75 and then just take the Turnpike. (Yes, I know I-95 is faster, but I want to avoid the Space Coast area for emotional reasons: My wife's sister lived just off I-95 in Viera, but she died last year, my wife took it extremely hard, and I'm not sure I want to subject her to passing that close to where her sister lived.)
BTW, in the Jacksonville area we normally use I-295 if we want to connect to I-10, FL-23, etc. west of town. Reason: The exit for JAX Airport is right around 690 miles from home, so that's an ideal distance to drive in a single day and we usually stop for the night there if we're taking I-95 south.