Like others have wisely mentioned already in the thread, function should dictate the form of the lid.
The Val Cushing Handbook has a great section on lids. There are drawings of all sorts of different shapes, do's and don'ts, critical mistakes, tips, etc. When teaching lids to my students I'll share these pages and frame the discussion around function, then over the course of a couple weeks cover (no pun intended) 5 lids:
- Basic Flange "The Hat" thrown upside down
- Basic Gallery "The Bowl" thrown upside down
- Flange + Gallery w/Inset Knob thrown rightside up
- Flange + Gallery w/Attached Knob thrown upside down
- The Russian Doll thrown as a closed form then trimmed gallery and flange
So many lids, so little time.
Someone also brought up firing lids atop their corresponding jar/teapot versus firing them separately. I'm all for firing lids along with their corresonding piece. Where the clay is going to experience change and movement as it shrinks, I want the set to experience all this change together as one piece.
My two cents.