Well, I played 20 years e4-only. Then both moves, now almost exclusively d4 (resp. 1.Nf3 or 1.c4). I find it "deeper", richer as well as more profound and more sustainable. Had recently won some games against decent FMs, so I'll stick to d4/Nf3/c4. I think Black has an easier life equalizing against 1.e4.