Since no one else has responded I'll take a stab.....
Of the six.....
1. Browning High Power 40 S&W
Advantage, power, reliability, accuracy, ease of shooting well, good sights, good trigger.
Disadvantage, size, weight.
2. Browning BDA .380 ACP
Advantage size and weight.
Disadvantage, bare minimum defense caliber, the gun is large for the caliber.
3. S&W model 66 .357 mag
What barrel length? Assuming 2 1/2 inches.
Advantages, possibly the ultimate CCW revolver, very powerful and can use any ammo from poppers to blow down the barn door, excellent trigger and can be improved further, great sights, unlimited types of grips, intimidating appearance, excellent "shoot-ability". A real fight stopper.
Disadvantage, weight, extreme muzzle blast if loaded with Magnum ammo.
Slower to reload and spare ammo is bulky if carried in a speedloader.
Easier carry in a "speed strip" but slow to use and too easy to fumble the reload.
Like all bigger, heavier guns requires a serious holster and belt.
4. S&W model 36 .38 special
Advantage, size.
Disadvantage, size. Meaning the gun is very small and easy to conceal, but the small size makes it harder to hold well and much harder to shoot well under stress. Trigger not so good and harder to improve easily.
Sights small and not easy to use effectively. Only 5 shots, and has the same reloading problems as the Model 66.
5. Tanfoglio TA90 9mm
Advantage, excellent feel, selective DA/SA trigger action, large magazine capacity, excellent shoot-ability, good sights, usually reliable.
Disadvantage, size and weight, awkward location of the safety.
6. Ruger Single Six Vaquero birdshead .32 H&R Mag
Advantage, none.
Disadvantage, no one serious carries a single action for CCW defense.
My personal choices....
Revolver, the S&W Model 66 by a country mile.
Auto, Tie between the Browning and the TA-90 with the Browning having a slight edge.
The Browning safety is better located and you get a good single action trigger all the time, plus the better caliber. Simply a better quality gun.
The TA-90 because of the DA-SA trigger.
Modifications...
S&W Model 66.
None really needed other then grips that suit you. That would be for feel NOT appearance. I use Pachmayr Professional Compac rubber models.
You could spend money on a trigger job (action job) by a good gunsmith but that's not really needed. The idea would be for a smoother trigger action NOT a lighter trigger pull. If the trigger is heavy, build up your trigger finger.
You'd need to do some serious heavy-duty reload practice.
Ammo.... If you want and can effectively handle full charge Magnum loads the 125 grain hollow point is the best, BUT it's also hard on the forcing cone and could cause it to crack.
Second Magnum choice would be one of the "short barrel revolver" Magnum loads in the 135 grain range.
A possibly better choice would be the Buffalo Bullet Company HOT .38 Special +P Lead, semi-wadcutter, hollow point.
This is loaded to near-Magnum levels and is what the +P load was originally before the ammo makers started downloading it.
This was the load that ended the .38 Special failures to stop problem.
Street cops called it the ".38 SPLAT" for the sound is was supposed to make when it hit.
Much less muzzle blast and recoil than a Magnum load, very effective.
Second +P choice would be a 125 grain jacketed hollow point.
Browning.
Grips that suit you. There are wide choices from rubber to woods, to synthetic. You can have attractive as well as effective types.
For a CCW gun trigger and sight work is really not essential with a quality Browning.
THE critical item is that the gun be reliable. Accuracy is NOT a factor, reliability is. Don't get lost in the accuracy idea.
TA-90.
Grips that suit.
Reliability. Trigger work and sights again usually not needed.
If the mags don't drop, you need to slightly bend the wide, flat spring in the magazine well. On the original CZ pistols that not only covers the sear assembly it's also a magazine brake to prevent the mags from free dropping.
Remove it and flex it slightly so the mags will drop.
With all guns... a good quality, good design holster that actually "fits" you.
Comfort is very secondary. Jeff Cooper said a gun needed to be comforting, not comfortable.
What is needed is a holster that conceals well, secures the gun well, is fast to use and most important; a holster that you'll wear ALL THE TIME.
A holster that is slow or difficult to put on will get left at home.
I've been informed by a man who KNOWS that the world's worst feeling is just running down to the store for some bread and suddenly realizing that you're in the middle of a life and death situation...... and your life-saving gun is at home because it was too slow to put on or you just couldn't handle some discomfort.
Wear a gun and holster long enough and it gets comfortable enough.
The same holds for a gun. A gun that's too big or too heavy will get left behind.
A gun that's too tiny can't be used effectively or won't stop a fight.
There's a range between a tiny gun that you can lie to yourself that you're armed, even if you can't hit anything fast with it, and a gun so large and heavy you just get tired of it and start leaving it home.
enjoy..
Just gos to show, old threads never die, they just turn into zombies.