I have used 50mg Viagra and 20mg Cialis and both work about the same for me.  The beauty of Cialis is that it builds up a level in the blood if taken daily.  One dose will stay in your system for up to thirty six hours.  Daily dosing of a lower dose will build up a level in your blodstream. If you go to the Cialis web site and look at the PDF for dosing (geared toward Dr's but very easy to understand) it will describe a daily dosing scheme of this nature. 
I prefer a daily dose of Cialis because I'm good to go anytime.  I also get multiple pops a day while on Cialis.  With Viagra I'm good for one orgasm per dose within a meager four hour window.  I use ancillary guys liquid Cialis.  I don't really measure it.  I just take about half to three fourths of a dropper or so every day... 
I'm 41 and my wife is 25, so I need all the help I can to keep up !! Of course with certain AAS, she needs all the help she can to keep up !