Okay for Jumping I almost always use boots here is why: They offer for protections, they come in many different shapes and colors, Open front or not open front. Here is why I don't use polos for jumping, if you don't know how to properly wrap them on a horses leg you will end up doing alot more damage then any good, potentail for it to come loose and start unwrapping itself in the middle of a course or over a fence can be highly dangerous.
Splint boots are a safer, easier choice :) You can get them in great colors and patterns too, even the SMB boots are good, more expensive but offer good portection and support, easy to wash and very secure! Davis, Roma, Weatherbetta, Dover all carry their own brand name splint boots.
When I use polos I only do it when I am on the flat or hacking out, some of mine are older so I like to be on the safe side and use tape to make sure the velcro wont come undone, they also come in great colors and patterns but you need to know how to roll them, how to apply them to the horse correcty!!! Takes a bit of practice, but in the long run I choose boots over polos for jumping :)
Some splint boots come with fleece lining or neoprene, good qaulity boots ussally go foor around 40.00-70.00 and if you take good care of them that lasta very good long time!