I personally prefer Cialis, it seems to take effect faster and there is less sinus, congestion, etc. Remember to take on an empty stomach (1 hr before or 2 hrs after meal). I have noticed a slight headache the next day and some low back pain if I took for several days. They work for at least 24 hours and for me work better after about 12 hrs than before. Viagra is hit or miss for me plus the congestion, etc... it has the same empty stomach restriction but does only last about 4 hours. For either to really work I have to be turned on anyway. Neither is like when I was in my teens and 20's. They say not to take while drinking, I'm always an advocate of physician advice but I've never experienced any side effects, this is not a recommendation for anyone to try this just my experience. I think Cialis hands down, although I will say that Levitra is my personal favorite but there is no coupon to get it. NOTE - if you can get your physician to prescribe you 30 of either at a deep discount at most major pharmacies. Enjoy.