I've managed to buy generic forms of Viagra, Levitra, and Cialis in Europe. I cut the 100mg V pills in half, which someone else upstream noted as well. On the half does, I still get as hard as a rock (sometimes to the point of desensitization) and the side effects are manageable. I might try 1/4 dose the next time and see what happens.
I tried one of the 20mg Cialis pills. The good news is that my erection seemed more natural. I didn't get as hard as with Viagra, but all the sensations were there and I performed normally. But, the side effects were pretty severe. I felt like I had the flu. I haven't gone back to Cialis. But, since I have a batch of them left, I may cut one in half and see what happens.
Generic Levitra was somewhere in the middle. All things being equal, I will probably stick with the Levitra unless the 1/4 Viagra pills worked as I hope they do.
I've found that the tiebreakers are: empty stomach, no alcohol, and stay hydrated.
PS: I haven't tried the gel versions yet, but I am told that they have less severe side effects than the pills.