I've had prostate cancer surgery and tried all three.  The only thing that works for me is Caverject (by prescription only).  I have to use a needle and syringe to inject a drug into the side of my dick to get a one-hour hard-on - it sounds a lot worse than it is, but for you guys who are using these drugs to enhance your erections, just be thankful that you can get an erection....and if you're getting up there in the 40's and 50's, make sure you get your PSA levels checked periodically.  Not being able to get a hard-on pales in comparison to being dead (although there have been times when I've thought seriously about those two options .  The up-side is that my surgeon wants me to get an erection at least once-a-week or more regardless of method used (use it or lose it principle) - what's not to like?