You could consider me "Old School", in that I like a pocket calculator. Notice I did suggest you consider a pocket calculator when you first asked, because I had mistakenly assumed you were a senior in HS (you did mention taking the ACT), and I figured you had no real need for a graphing calculator at that point.
If you have a real LOVE of math (and only a passing interest in the other sciences), the Ti-Nspire is a great math tool. However, if you need to crunch numbers and use the calculator to crunch out problems relating to real world math, a graphing (or any) calculator will provide you with a better number crunching interface and support your needs for advanced math functions ie you learn the math and then use the calculator to crank out the answers. The Ti-Nspire has a teaching type interface as well as the number crunching mode. I suggest you research a few you-tube videos to determine this subtle difference. The original Ti-Nspire used to offer a Ti-84 keypad to bridge this gap in differences, the new Color versions do not offer this, therefore, you will have no keystroke equivalent to the Ti-84 series to follow along in your classes. Probably not a big deal, but something to be aware of.
Admittedly, your own needs might lead you to choose the Ti-Nspire, it is the more capable (powerful) device. But at the HS level, your teachers and other students are much more likely to have, use, and know the Ti-84 calculator.