If you go to the link below, it shows pictures of muzzle flash for various calibers with various size bullets. It is by no means an exhaustive reference but it does show enough information to make one question statements about which caliber produces the most muzzle flash. The only definitive way for anybody to say that one caliber/pistol has less muzzle flash than another caliber/pistol combo is for a person to shoot both under equally dark circumstances.
Choosing which CCW pistol/caliber is right for you involves a lot of differing factors and as always, should normally come down to which one you feel most confident with and can perform best with. There are exceptions, such as when you have to carry a sub-compact size (probably a .22, .25 or .380 due to pure small size requirements) but in general, your choice should be dictated by what you feel most confident with and what you shoot best.
If I was in a shootout at longer distances (50 yards plus), a 1911 style pistol in .45 would be my 1st choice, followed by a Glock 22 in .40 (I used to shoot it at 100 yards fairly well). A Glock 35 might be a consideration also but I have never shot one.
If I was in a gunfight at shorter distances (under 50 yards), I'd probably choose a Glock 22 in .40 as I've already survived one gunfight with this exact pistol.
If I carry CCW in a gun-bag or in a belt holster covered by a shirt, I currently use a Glock 30SF in .45. If I'm dressed ins slacks with no belt holster opportunity, I stick a Walther PPK/S .380 in my front pocket. Not my preferred gun to shoot (although it's quite accurate at 15 yards or less) but the trigger is a little stiff.
My point is that different situations call for different guns/calibers. As you experience more situations, your opinion(s) will change and there will be occasions when your preference simply isn't the best option.
I'm not denigrating a 9mm as I've carried one (Glock 17) on and off-duty for a few years before switching to a 45, then a .40 and back to a 45. In the future, I may add a 9mm. Who knows?
My point for the OP is to make YOUR best choice and re-evaluate from time to time. Don't lock yourself into a single caliber, make or model. Practice with everything you have and think your way through what YOUR requirements are for each CCW situation as your requirements/situation may vary from mine or the next persons.
http://www.luckygunner.com/lounge/muzzle-flash/