Depends on what you need one for. Not a lot of detail on the specs. Some considerations for you: How much weight do you want to carry? Where do you want to carry the weight? You need to decide for yourself how much water to carry as the weight soon mounts up. I've used both Camelback and Inov8 and prefer the Inov8 as the weight is carried closer to the hips - it just feels better (to me) when running down steep slopes.
This is good enough for me: http://direct.tesco.com/q/R.100-0611.aspx
That tesco bag looks top value! I have the mule for full days out on the MTB, or the classic for shorter rides. But to tell you the truth i have been using a cage and bottle with a tube in my pocket just lately. Think about what you are going to use it for. I used to guide rides and needed to carry first aid, spares for multiple people and food. The more space you make the more un necesarry (sp??) crap you carry.
http://www.manxfellrunners.org/
My island is very nice
I don't need much wieight that's why i prefer these models. I think the Tesco is much heavier. I think up to 2lt of water is enough for me so i set the maximum to 2.1lt.
The Tesco is pretty light but only takes 1.5 litres of water.
http://www.tredz.co.uk/.Camelbak-Rac...2009_24876.htm
what about this?
i have a camel back which is very comfy riding your bike or walking, but for running it bounces about far too much i recommend the inov8 racepro 12 with bladder if you plan wearing it running.
slow upfast down
I was thinking of the fairfax which has an insulated reservoir pocket so it can keep the liquid cold for more hours.