When I'm heading north from Ft Lauderdale, or heading back to Ft. Lauderdale area from up north, I normally use the Jupiter exit on the pike to switch from the tpk to 95 or the other way around.(Did that make sense?:B)
95 through West Palm can be 4,5,6 lanes of "crazy" and stressful (so many on and off ramps). A section of the tpk is only 2 lanes and can be a problem, if there is an accident. That being said I prefer the tpk.
Since you're staying at Treasure Coast, it looks like the easiest thing for you to do (aside from the cost) is to get on the tpk. at the Ft Pierce exit. Take that all the way down the pike, to the Tpk. extension which will drop you off in Fl City on Route 1, right at the start of the keys.
Regardless of how you get there, I suggest you get a Sun Pass for the tolls. The tolls along the extension, among other sections of the tpk, don't have toll takers, and the they will bill you by plate through the mail , which could be a hassle, besides being more expensive.
