I had a .22 for a short time, but never shot it enough to determine a favorite. Of the 3 .177's I've owned, JSB Exact 8.4 in the 4.52 head size, or Superdomes were the best. The Superdomes were usually a little faster, but not quite as accurate.
For short range work, my first CFX liked the JSB S100 match ammo, but I don't know if anyone has that in stock anymore. It also had a brief love affair with Crow Magnums, but that didn't last past my first tune-up.
My last .177 is now a .20, but since it's an LW, not a Gamo barrel, I don't suppose it's preference matters
. However, it seems to like FTS/FTT's the best at the moment. I say at the moment, because it's still a work in progress. Later.