I've tried and prefer Cialis myself. I've enjoyed the benefits for at most three days, not as strong on the third day, but still noticable, for me.
Viagra gives me a nasty headache, Cialis not so much and this goes without saying but I will say it anyway, check with your doctor and read the product warnings.
I haven't used it for about three years but found it helpful.
...and just because this is my first post since April, No I don't work for any drug company, it's affiliates, nor do I receive financial kickback in anyway from this post.
Did I miss anything...never mind, forget I asked!