Viagra makes it harder?

Pfizer are claiming their drug provides more rigid erections than
their competitors but this is difficult to assess from patient
reports. What are your impressions of Viagra, Cialis and Levitra? Have
you had to switch between drugs to achieve better rigidity? Have you
had to employ any other techniques to improve the rigidity? It would
also be interesting to hear from real patients on the use of Cialis
and it's duration of action; can it really be over 36 hours?