If you sit on the left side for both outbound and return segments, you can get the best of both worlds. On the way in, you'll get neighbor islands and then Pearl Harbor. On the way out, you'll get Waikiki and Diamond Head.
Sitting on the right side for both segments wouldn't be as good. You'd get Waikiki and Diamond Head on the way in, and neighbor islands on the way out. (Reverse of above) But you won't get Pearl Harbor nearly as well from the right side unless you take off to the West, which is uncommon.
So I'd do left side for both flights. As an added bonus, the city view will be more interesting as you leave and are more familiar with spotting landmarks or your hotel from the air.
cnk