I keep mine at 80-82, but it really is just personal pref. Supposedly 78 will give a longer life, but then again, that could depend on so many other things as well. What if being warmer prevented ich or some other parasite?
Now that I think about it, not sure if higher temp is better for beneficial bacteria growth, but that is something to consider for water quality. Maybe someone who has more experience with that sort of technical stuff could weigh in. Of course clean water and just being warm at all are going to give you good results.