Hi, not sure whether you want a horse one or human one? Anyway if its human then these guys are really helpful and reasonable - you should be able to narrow it down, perhaps one of the active max ones? But one of the most important things is being able to use it!
We've got the Standard 40 First Aid Kit (High Risk) and I have a husband who has done the First aid training. Its situated on the wall in the tack room and anything that has been used has to be replaced as quickly as possible because when you really need it it won't be there.
Bear in mind a lot of things in kits have use by dates so you should check them regulary (we put them in our horse kit when they are out of date)