I have alwasy enjoyed using semi-fluid tripod heads and have had a number of Manfrotto ones over the years. Models 501, 503 and the latest was a 516 I think. I find them very smooth when following a subject and the fact I can let go and it stays put is brilliant. Their weakness is they do not last and every year need servicing. They either go too tight, due to the dirt and muck that I find myself working in, or too slack and they start to wobble.
Finally I have given in to fashion and gone for a Gimbal type head. They are very popular with wildlife photographers and I see them everywhere. From America I have bought the Black Widow by Jobu.
Now I am wondering why are they so popular. There were no controls on my Manfrotto head, you just pushed the lens where you wanted it to go, let go and it stayed still. Now I have to adjust two controls everytime I start. One for up and down and one for panning left to right. I find it a real pain to have to do. With fine tuning I can set it so I can let go and the whole thing does not tip over, but it takes time. When I pan the movement is nowhere near as smooth as with my fluid heads. The Manfrottos were dampened and I found quick movements to compose the picture much easier to do. With the gimbal I go past the point and have to return.
I still have an old German fluid head in my cupboard. It is very old, high quality head and the tripod is past its best, but if I can find some new legs maybe this is the way to go. For now I will try and get used to the gimbal.