Indian creek .555 .562.
Sumtoy .562-5
Carlson's .565 .575
Long beard .568 (made by Carlson's)
JEBS .560 .565
Promos tightwad .570
I could go on and on but honestly I matters on what type of pattern YOU are lookin for. Super hot core , hot core with a more forgiving pattern in the 20" ( 70/30),or more even #s in the 10"/20" 60/40 or even 50/50. I've named a few starting points and truth be told it's more trial and error than anything.
If you look around on the forum and even places like midway USA towards the end of April and into May you can find some really good bargains on all kind of choke tubes. Good luck brother!!!