just take all your EDC items, and toss them all into a plastic bag.
this will give you an idea of what size bag you need. take the largest item and get a bag around that, ie: an ASUS 1005 Netbook. once you figure out the space needed for that, the rest will follow.
personally for me, i will be going with a maxpedition colossus. i looked at the jumbo & fatboy; for me, they weren't 'modular' enough.
for example: id rather add an exterior pouch(zippered) to a colossus rather than have a bottle holder(like the jumbo). i REALLY like the 10x5 bottle holder.

: then on the other side i can put something else, like a first aid pouch. this will leave the rest of the interior of the colossus for the rest of my gear.
the only thing i dont like about the colossus is that it has velcro on the front of the bag; i'd rather have molle attachment points for more options.
while the jumbo is great, i prefer to have options.
my hardest decision is what color to choose. black is too tactical, and gets dirty real fast. green looks to military, so that leaves the tan. i wish they had grey.
this is for my EDC or get home bag. NOT to be confused with my BOB.
good luck with your search. mine is over.

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