Some folk swear by the stirrup pumps; from what I've read the hillspump with the drypack filter seems to be the best- as the only real difference between using dry-air from a divers bottle and a hand pump is moisture getting into the air reservoire and causing rust! Something which will not happen when using dry divers air from a dive bottle.
Other factors include: a dive bottle needs to be certified as safe every so often, and you need a diving shop (etc) that will allow air filling for non diving purposes (some shops don't), also you gotta be able to fill the dive tank to 300bar (some differ, but from what I've seen that's the most popular).
But after all of that, I guess it's a question of how lazy you are! It's about the same price for a hills pump and filter as it is for a 3L 300bar tank (with guage and assiciated hoses). For convenience I'd go for the hand pump, but given the choice the divers tank would be best for air quality and ease of charging the gun and a dive bottle refil shouldn't cost more than a fiver