I've been using a TI-84+ Silver since the 7th grade, 6 years ago, and I am in college starting electrical engineering next semester. A lot of calculus and physics stuff as well. So, with some newer models available I'm thinking it might be time to upgrade.
Should I? And which model?
I took both physics and astronomy courses at the university and my TI-84 Plus was more than enough for those courses.
I really don't think you'd need a more powerful graph-calculator.
Also, switching brands is generally not a good idea, CASIOS have an entirely different UI and method of inputting shit. If you are well used to the TI, then I would go against changing to other brands.
All in all, the TI-84 should be waaaay plenty enough
No need to upgrade. I myself have a Ti-Nspire with a Ti-84 keyboard, and I have not yet seen any mathematical calculations it cannot do on the Ti-84 keyboard. I'm going to probably stick with this through college (I'm in high school right now) as my school district sees no reason to upgrade from Ti-83s as they are already powerful enough and my Nspire keyboard has functionality that makes the Ti-84 keyboard seem like a bad joke.