You have a pretty broad list of how you want to use it. IMO, a good commuting pannier doesn't make a good grociery pannier, and a good grociery pannier doesn't make a good touring pannier. For commuting, I use the Novara Commuter Pannier. You can read my review here, it addressess most of you questions:

http://www.rei.com/product/780448

For things like grocieries, I'm more inclined to put a folding basket on the bike, or maybe a softside basket style pannier.