If it's mostly just practice, I'd recommend something where you load the arrows in point first from the front.
The Chief side quiver (and side stalker and all similar ones) works great, as does the Arrowmaster and Dawgware quivers. Where they fall short is on the range shooting lots of arrows. Putting an occasional arrow back in them while hunting or roving is easy, putting a fist full back in however is not. I have a Dawgware (and if I didn't get that before the Arrowmaster came out I'd have the Arrowmaster) and like it for hunting in dense brush. Keeps the arrows completely protected and you can get one out with very little movement. Great for if I'll just be hunting big game and will only need one arrow or the occasional stump shooting.
For general use and hunting where I know I'll be shooting lots of arrows though (small game, which is most of the hunting I do these days) I use a Plains style side quiver. I'm biased though, since I make 'em and sell 'em (see the Classifieds for some examples)
The standard type of belt or hip quiver work great for the range, but I can't stand trying to hunt in them.
If you ask 10 people what the best quiver is you'll get 10 answers. Try them all for yourself and see what works best for you. You can make a basic practice plains quiver or belt quiver in about 10 minutes from a pair of jeans. The tube style side quivers can be made in about the same time from a large cardboard tube, map tube or PVC pipe. Play around with those cheap quivers to see what you really like before dropping the $100+ on each of the commercial ones. Wish I did..
Then again, we gotta keep the economy going LOL!