Which one is better in terms of features, ease-of-use, and performance?
I have used both and I find biteSMS to be the superior app. I have no scientific data to back that up, but in my experience biteSMS has performed flawlessly while I always had trouble with iRealSMS. It may be different phones, but I used iRealSMS on a 3GS and gave it up, then moved to an iPhone 4 and installed biteSMS. I haven't looked back since.