I agree with Terry, each situation is different. I have bow quivers, back quivers and side quivers. The one I use least is the side quiver. I find it takes too much movement to get an arrow out and onto the string.
The fastest to reload is the back quiver. I take the arrow out by the nock, lay it across the bow, nock the arrow, and shoot. I can do all this without looking at anything but my target.
I don't care for bow quivers on my longbow, so when I hunt with it, I use my Hill style back quiver. I do like my Selway limb bolt quiver on my 3 piece recurves. It is light enough to not overbalance the recurve and allows me to carry five arrows. Like the side quiver, it is not quite as fast to get into action, but as has been said, it is one less thing to forget.