It is annoying to go to cover a full pail and realize the lid is the wrong size!
I have mostly 45-lb pails, a bit shorter than the 60's.  They are mainly
from bakers and doughnut shops, and contained fruit or pudding
pastry-filling.  The few 60's (5-gal) pails I have were received from honey
packers or other beekeepers.
 
I like the either the 45 or 60 lb size.  Ideally I'd have all 60's.  The
smaller ones will hold 50 lbs. if filled to the top, usually.  Then you can
sell it as a 50-lb unit.
 
There are two different shapes of the doughnut filling pails that I have,
which can be frustrating. You have to separate them before you stack the
empties, or they will get stuck.  One design is more or less like a 5-gal
pail. in diameter, whereas the other style is broader and shorter.  The
lids are quite different in design and seal.  I tried to stick with only
one style pail, but after lending pails or having extracting done
elsewhere, or selling to small-scale packers, inevitably things got mixed
up and I lost standardization.  Oh well.  Now I'm just glad if I have
enough pails, period.  Four bucks apiece for new ones is pretty steep --
maybe theres a good discount if you buy a large number.  Anybody know of a
good source that is more reasonable?