I really love my camelbak -- small, 50 oz. backpack style. Here's why:
I can't stand to run with anything around my waist.
I can't stand the sound of a water sloshing in a bottle.

My camelbak is very stable. It fits close but is not binding. There is a strap that goes across the chest, so the pack doesn't bounce or anything. It doesn't have any effect on my arm swing. If you bleed the air from the bladder after you fill it, there is no sloshing at all. The pack is lightly insulated, so drinks stay cool-ish.

I have both a North Face hydration pack and a 4 bottle Nathan belt. I almost never use the Nathan... it just bounces around too much. The water sloshing around in the back pack is a pain, but you just have to keep removing air from the bladder to fix that. Another added bonus of the back pack is that you can take the bladder out and use it to carry whatever you need (spare socks and boxers for my work commute).

George

This is good stuff - I was originally looking at waistpacks, now this thread has me looking at hydration backpacks. My only dilemma now is choosing between 50oz or 70oz, hmmm....

There are lots of discussions on the Net about this very subject. There are pros and cons to each type. Here are my thoughts:

1. Hydration packs. I have 50, 70 and 100 oz packs (CamelBack and TNF). Convenient and hands-free. But HEAVY (esp. the 70 and 100 oz). It takes several weeks to get used to the weight, and the first week or so your legs will suffer and your feet and ankles will feel pounded as your pace slows a minute or more per mile. You sweat a lot more with a backpack b/c they block the air flow to your back; this causes sweat to run down your back, saturate your shorts, and run down your legs where it pools in your shoes. You can try getting wrist-worn sweat bands and putting them around your ankles; this works if you can find big enough ones. Because of the weight and sweat factors, I only use a pack if I absolutely have to, i.e. no water is available for a couple of hours. I've only worn mine once this year and it was not fun. Oh, and the backpacks can cause rubbing on your technical shirts which can kind of ruin the fabric.

2. Waist packs. They don't cause as much sweat as backpacks. Usually you can only have a 40 or 50 oz max, too, so they have a more limited capacity. But the bouncing drives me crazy. I usually don't wear one unless I just feel like something different.

3. Hand-held water bottles. I can carry 2 20oz bottles easily (or even 2 26oz bottles). And if I want to, I can carry a third without too much bother, totaling 60 to 75 oz. Your hands and arms have to get used to this (esp. the 3-bottle option). However, with 2 bottles, they provide a nice counter-weight and feel good and balanced. There is none of the bounce or sweat factors from waist or backpacks. But as with the waist packs, there is limited capacity. This summer hand-held bottles have been my first choice: I usually carry 1 20oz bottle filled with sports drink and another 20oz bottle filled with sports drink powder. Every 20 to 45 minutes, I put a scoop of powder in the empty bottle and fill it with water (free from fountains and some fast food restaurants, or I buy water in convenience stores).

4. Carrying nothing, buying Gatorade or water along the way. By far the easiest solution, provided you're running through a city. If the convenience stores are sparse, you have to plan your route around them. The cost can add up too, at $2 for a 32oz bottle of Gatorade. If it's really hot and humid, it's a real pain having to seek out a convenience store every 20 or 30 minutes. In the winter, though, this is by far the best option and what I use almost exclusively.

5. Convincing your boyfriend or girlfriend to meet you along your path every 30 to 60 minutes... I've never been able to do this, but I fantasize about it. Oh well.

Having only ever run with a Camelbak waist pack, here is my experience. Bouncing was only a problem until I figured out that I needed to wear the pack on my waist, and not on my hips (i.e against the small of my back). The sloshing drove me nuts until, as others have pointed out, you remove the air. I've got a FlashFlo, which holds 48oz of liquid, and I try to route my runs by potential refill stations. The biggest hassle for me has been getting the drinking hose balanced in the clips so that it isn't whacking against my legs or arms.

I just got a Camelbak Catalyst and like it. I did a more comprehensive review at ltft.blogspot.com, if anyone is interested.

Harper -

The "nipple" type top on those wigged me out a bit I have the Nathan bottles...not easy to pop the top down again when I have both in my hands, but doable.

I'll keep messing around with two bottles on my longer runs with no refill options. Good to know it gets better - thanks!