i would think that depends on where you have them hosted. i use photobucket because i can upload 1024KB images, and they give you 1GB of storage and 10GB monthly bandwidth for free. i also believe you can make any number of sub folders with an account too. i havent had a problem with my bandwidth being used up there, and you can always make more accounts if you need to.
if you wanted more storage/bandwidth, you could get a "pro" account there. its only $25 a year and then you get 2MB image uploads, 5GB of storage, and unmetered bandwidth.
i dont know how any of the others work so i cant offer any suggestions other then photobucket. i have an imageshack account too, but theres too many times where they are real slow to load images, if they get loaded at all. for me, photobucket is the way to go.
hopefully this helps you. if not, im sure someone else will eventually post here and offer their suggestions too.