SuperKen, you're half right and half wrong.
2 120's will move more air than 3 80's. It typically takes 5 80's to move as much air as 2 120's of the similar model.
But you're not necessarily right about the noise.
I just modded a smallish case with major size limitations but was able to fit in 6 80mm L1A's (4 intake/filtered -- 2 exhaust unfiltered). I wanted it to be as quiet as possible but still move about 60CFM through my case. It is much quieter than I expected. Since I was debating between 120's and 80's, let me share what I learned.
3 80mm Panaflow L1A's are quieter than 2 120MM Panaflow L1A's. In fact, 3 of these smaller L1A's are quiter than 1 120mm L1A!
Every time you double a fan's noise (by putting in another one) you add 3 decibels of sound. I've found this using a forumla I found on ARS and although it isn't exact, it's a nice easy to remember rule of thumb.
The 80mm L1A = 24CFM/21dB
The 120mm L1A = 69CFM/30dB
Therefore, it takes 3 80mm L1A's to equal the output of 1 120mm L1A. But the triple 80's are about 75% as loud as the single 120.
Another factor is that 80's are a lot cheaper than 120's. I got my 80mm L1A's from Teamawe.com for $4.75 each. Their 120mm L1A's are $15. So 3 80mm fans producting the same airflow are cheaper than 1 of their 120mm cousins.
I recommend 80's if you have the space for a bunch of them and are interested in being quiet! If noise isn't a problem, or you just want big fans, then use 120's.!