I support your choice for Irvine or NB. Yes, you can find apartments for less in other cities but I suspect that you already looked at those areas before nailing down your choices and that you are comfortable with the amount you will be spending on rent. Now, to answer the question you asked...
Based completely on road biking, I would choose Irvine. Irvine gives you a bit closer access to more rides...For instance it's at least 7 miles closer to Santiago Canyon or a loop around El Toro Marine Base. You still have good access to Newport Coast, and the SGRT runs right through it.
I lived in Newport for a short while during my younger days and I've lived in Irvine for 16 years now. If you have other questions, feel free to ask.
P.S. My wife told me to tell you that (if you're single), you'll get more chicks in Irvine or NB than those other places
