I'm looking at either the TI-89 Titanium or HP 50g. Which of the two is better? I'm taking digital and AC next semester and would like a good calculator for classes.

 

something that can do complex numbers and different number systems should do. I know the ti-89 can do it....

 

If you get a chance play with both. Sometimes the little things can be very aggravating.

 

It has been a while since I played with an HP calculator. Do they still use the RP entry method?

 

I've been using the CASIO fx-991 for my entire university career and my last couple years of highschool as well. It is a great calculator, can handle complex numbers in different forms, as well as decimal, hex, oct, and binary bases. Can even solve simple differentials and integrals, and has 40 of the most common constants built in.

Highly recommended and only ~$20.

 

Both of the calculators you've mentioned can be a handful and maybe not even necessary for first year AC and digital circuits. I'd take the advice given by Bill Marsden and find a shop near you that has demo units. Go and play a bit with all of the scientific models and see what you think.
I usually advise first year students to try the Casio that Dalaran mentions or something similar.
If you don't like it or find that you MUST have something more complex, you've only lost $20.00
The HP 50G can be overwhelming for some, and it costs plenty. Odds are, you'll not most of it's features, especially if you are beginning your schooling.

 

I'm looking at either the TI-89 Titanium or HP 50g. Which of the two is better? I'm taking digital and AC next semester and would like a good calculator for classes.

I would suggest an HP! It can be handy at higher level courses in digital systems. Please review the following link:

http://www.ncees.org/Exams/Calculator_policy.php