I'm not sure which fluid my 2006 Civic came with from the factory ... MTF I or the thinner MTF II but when I switched to Amsoil MTF, I wasn't too impressed. It was the middle of summer and, initially, I felt that the factory fill was a bit smoother. But after 2-3,000 miles of warm weather driving, the temps dropped and winter came. The sub-freezing shifting was MUCH smoother and by the time the next spring and summer came along, that became smoother as well.
I now have about 55,000 miles on the fluid and the shifting remains butter-smooth. I will probably swap out the fluid again within the next year but it's NOT because the shift-feel has deteriorated.