Should I buy a backpack or bicycle bag?

Looking to replace my marmot day-pack as a bicycling commuting. Should I go with the Timbuk2, or a bicycle specific backpack. Brand suggestions? Personal experience?

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1. Where I live, I simply tie the grocery bags to the handle bar or top-tube
   of my road bike (limited load carrying capacity on road bike)

2. The best type of bag for commuting is one that attaches to the bike, a pannier or rack top bag. If your commute is short( under 10 km) any backpack will do as long as it fits well.

3. just any old back pack should be fine
   unless you are carrying half a car;s worth of stuff for 50 miles
   short distances, light stuff, back pack wins the game
   just my experience
   no fastening / unfastening /loading/unloading
   cheap
   when you get off the bike, your stuff comes with you

   i don;t get the fascination with ‘messenger bags’ either
   unless you are an actual messenger and have to get stuff in and out in like 2 seconds, 50 times a day
   they just keep sliding around into the wrong place, is what i see people fighting

   wle.

4. I own and use both a small bike shoulder bag and a larger bike messenger bag (Da Kine). Both work fine and are relatively comfortable, BUT for regular use I recommend a rear bike carrier (with bungie cord) and a carrier top bag and/or waterproof panniers. The advantages include a) they don’t put the weight up high, b) allow more capacity, c) are less likely to leak in rain, and d) adapt to the amount of material to be carried (use zero (carrier top), one or two panniers).

   While messenger bags are useful, one disadvantage is they always seem to need "adjusting" every few miles, and if you take a tumble can be a hazard (I got cut off by another cyclist on a bike path, came down on my back on top of the bag and crushed two vertebrae partly due to the pressure being concentrated on the (hard) contents of the messenger bag)

   I use the messenger bags for occasional trips on my good road bike (which doesn’t have a carrier) for when back pockets in a cycling jersey are inadequate.

   I have tried backpacks, but never found them comfortable since the straps inevitably pull back on shoulders.

   Cost wise, panniers and a rack are a bit more expensive ($150+) than even a good messenger bag (~$120), but are more flexible (you are even set for some limited bike touring) and have some advantages. That said, there is a place for both.

   Hope that helps.

5. i used a Timbuk2 messenger bag, of course they are designed for riding, but I usully had a full, heavy bag, and had to stop to switch shoulders. get a backpack