Important question. Until I took my major DiNotte plunge I was going for the tail light only since I ride at night on fairly empty windy country roads. I figure I can see and hear someone coming and drive very defensively if I feel worried by them, but if somebody zips round a corner and I have not heard them... I want them to KNOW I am there. So for me, DiNotte tail with a flasher too.
I'm struck by the statistics tsl quotes. But if I hadn't been able to swing front and back I probably would have gone with what Varusceli suggests, DiNotte tail light with a Fenix on the front with the hopes of an upgrade later. Really think about the specific conditions you'll encounter since that will make all the difference. Good advice from everyone here, though. And they know whereof they speak.