I like to use them all in some kind of rotation, in a typical day I would use 2 to 4 pieces. One dedicated for oils when I'm having some and 2 or 3 for flowers. If I feel like taking big fat rips I go for maximal diffusion and if I want taste I go for small pieces or dry hitting. Sometimes I want a good compromise and I choose medium sized pieces.
It's also about how convenient they are to handle and to hit. In a lay back mode I want a piece easy to use so I don't break my neck.
It may seem ridiculous to some but in fact they are very different, each piece gives me another experience.
Right now I'm going for the matrix. I have been eating a lot of that home made pizza and I need a strong digestive.
Edit : I'm waiting for a new worked recycler ! My first heady custom
And more stuff.