Open front boots definitely. I only use polos when i flat because they offer no real support
If you are jumping, I recommend open front boots. They cover and protect the tendons and ligaments, but allow the horse to feel it if they hit the fence. This is important because if they can't feel it, they can become lazy/insensitive and are more likely to have rails down.
Depends on how sensitive your horses skin on their legs are. If they are really sensitive, go for wraps.
Polo wraps. Or like a splint boot of some kind. Open front boots have no protection in the front... so if your horse knocks a rail the polo wrap will protect them