If you get a Maxpedition, get strongside. The last thing you need is a thug getting the drop on you and taking your bag along with your firearm. If you get the strongside, I suggest not getting the velcroe holster, and carrying a revolver in the firearm compartment - If you get a bad vibe somewhere, you can unzip, reach in, grip the revolver inside the bag and have the drop on anybody without anyone ever knowing. The revolver can function inside of the bag (I think a semi-auto will get you one shot from inside the bag, maybe more, but I think it could/would malfunction). Granted it is from the hip, but if you are weak side and somebody targets you, go ahead and write them a check unless you want to run the risk of a brandishing charge.
A holster draws faster than the bag.
For something comparable to the Maxpedition:
http://www.ebags.com/mountainsmith/l....cfm?N=2008230
I prefer the Mountainsmith to Maxpedition. I like the older versions.