It depends on what type of boot you are talking about, what that boot is intended to do and what shaper the animal's legs are!
Just because you are show jumping does not necessarily mean you have to boot. But some horses can brush or over reach in the excitement of it all and so want boots ro protect against that. If you are going higher you might want a tendon boot to protect the front tendons from the hind shoes in a bad landing. You might have a horse that knocks his hind fetlocks together as he squirrels over and so needs fetlock boots.
First work out what you are trying to protect against - and then wonder what make of boot. All boots risk over heating and then weakening the tendons. Far better not to boot unless you need it.
(And in case you were wondering we compete BS with several animals from JC to JA. Only one currently has boots - open front tendon - because of the height and he has a Tri Zone pair and a leather caldene pair.)
Another vote for Veredus! Fit snug round their leg and very protective. Can be pricey but you can pick up second hand pairs for less. Definitely worth paying for though.