Well, all depends on your timing. It is a fine road after about 9:30 -10. If you get the fast pass you can breeze through most the toll plazas without stopping. I live about 10 minutes from I-75 and you never know what the traffic will be like due to all the construction starting at SR-52 all the way south past Brandon. I-275 is under major construction starting just north of down town. Just about backed up at any time of day.
What is your destination? St. Pete or further south?
If st. Pete, take the toll road, just make sure you are after 10.
If further south (Sarasota) I would take I-75.