anvil 30 vs lh 55 vs sirui k-40x 54mm ball head

I dunno about the LH 55 but I used to run a K40X and now I run an Anvil-30. I compared them both side by side and found the Anvil to be more stable. I also much prefer having just the one big lever on the Anvil instead of all the knobs on the K40X.
 
The LH55 and the Sirui ball heads have a “panning” feature which is not found on the Anvil. Depending on your use, panning may or may not be something you need. I find it useful for spotting but not so much for shooting. YMMV
 
There are several differences, but here's one. The LH-55 and Sirui are both manufactured for the photo market. They have significantly more parts for fine tune control. All those parts need tolerances which have to be "taken up" when the ball lock is tightened. This can actually be seen through the scope as POA shift.
The Anvil has fewer parts, tighter tolerances, and there is solid contact between the rifle, head, and ball during operation, and I've found it results in essentially no POA shift.