Boots are easier but if you plan on leaving boots on you're better off with polos. Polos are a lot more breathable whereas boots can cause bowed tendons, swollen legs and a bunch of other things when left on for an extended period of time.
Boots they're easy and safe I feel they offer more protection they're boots for every event where as polos aren't The best for all diciplines and take longer to dry if they get soaking wet
Boots! I can't wrap a polo to save my life... plus I'm not convinced they are useful, they just look pretty.
I prefer boots, one cause they are much easier to put on and two because I've seen way to many people put polos on incorrectly. I myself do use polos occasionally, especially when working with a horse I don't have boots for but would like them to have some sort of leg protection, but my number one go to is always my dsb boots for flat work and my open fronts for jumping
Boots, they are eaier to put on and safer bc pools are eaier to mess up and if you mess up you horse can get seriously hurt.
I prefer boots as they offer more stability on their legs, for example brushing boots, I find polos become messy and undone if a horse brushes his legs too much :)