I have both an inside tub with jets and an outside spa. The house came with the tub, I brought the spa from a previous home. Before I shelled out the bucks to install a new inside tub with jets, I would seriously look at going with an outside spa, if you have room. First, for renovations like this, you can wind up having to spend a lot of money to redo tile walls, floors, etc. Add that to the cost of the tub and you're well on your way to a real spa.
The tub has to be filled each time you use it. I don't think a heater is needed, because you likely won't spend that long in it. If it starts to cool, you can always add more hot water. Of course, that's another drawback, you have to fill it, wait and watch it, and all the hot water energy is wasted. And if you're just replacing a std size tub, you barely wind up with enough room for one person.
The outside spa can seat several people comfortably, is always available, and is far more enjoyable to spend time in. I use mine throughout the year. It's great for parties, having a few beers and smoking a nice cigar. Plus, depending on where you put it, the installation may be as simple as running a 240V line to it. They have timers so you can program it to stay at a lower temp most of the time to save energy, but rise at times of the day when you may want to use it. All in all, I think they are far more practical.