Either can be useful. The .38 snubby or .32/380 ACP you have with you is better than the .500 S&W you left at home. ANY hole you put into an attacker is better than wishing you had a gun! Personally I carry an auto, but have also USED a small revolver to defend my life, so I an speaking from personal experience, not wishful thinking.
The snake shot is not much good past ten feet for ANY use, but at very close range (car jacking) a face full MIGHT be useful to blind your attacker. Depends on if you are that cool, that accurate, that skilled. Don't kid yourself, 99.9% of the people out there are not, including the ones here. Plus if you are caught and it got out you intended to maim your attacker "for fun", you will be in prison so fast you won't believe it.
Think you are God's gift to gunning? Go to your local IPSC/IDPA shoot and try it. Can you pull the gun from the holster and get six aimed shots off in three seconds or less? I can and I'm not all that fast. Yes, with an electric timer and hands over my head. Alot of shooters go to pieces when being timed and watched, but "if they were on the street they would kick butt!!" Yeah, right. You can't handle the pressure of being watched and timed, but fighting for your life makes you better under pressure? Pardon me while I laugh.
ALL guns can jam, Glocks, revolvers, etc. If you think YOUR gun can't jam, it just means you don't shoot enough. I personally have seen three Glocks blow up. When Glock blow, they are completely trashed. When a 1911 blows (I had one do so while I was shooting it, probably a high primer) NOTHING was serious damaged! After knocking what was left of the case out of the barrel, I continued to shoot. Does this mean the 1911 is better than the Glock? Of course! Does this mean you should get rid of your Glock and get a 1911? Of course not! Wait until the Glock breaks (if you shoot it, it will) and THEN buy a 1911! Why don't Glock owners know any good gunsmiths? Because when a Glock breaks, they buy a 1911.
OK, only SLIGHTLY kidding!! If you like Glocks, than carry a Glock, but don't buy into the BS that Glocks are the end all and be all of handguns that so many Glockheads claim. They DO break. When they break it WILL be a pain to detail strip and get parts for. When they blow, they are normally completely trashed. They can't handle lead (the polygonal rifling will clog and then the pressures build until the gun explodes) so you have to use only jacketed ammo, which makes it less than optimal for survival/back country/out of country use that some of us subject our guns too and you use what you can get, or do with out. YMMV.
The gun you have WITH YOU is better than the gun you left at home.
Use the best FACTORY hollow point/Glazer/defensive ammo you can get, not snake shot.
If it was made by humans it WILL break, at the worst possible moment of course.
PRACTICE, PRACTICE, PRACTICE! Join your local ISPC/IDPA/shooting club and LEARN!
Buy a quality holster to carry your gun, not some piece of floppy crap.
BUY AMMO! RELOAD! With the demonrats getting in and the price of copper/zinc/lead going sky high, there has never been a better time to learn to reload and stockpile all you can of powder, primers, cartridge cases, as well as loaded ammo. It isn't going to get less expensive and may get banned competely.
If you think the idea of ammo getting banned is far fetched, just look at the ammo bans introduced by the deamonrats already. The Commie-fornia $1 per bullet tax bill (just think what that will do to a box of .22s!), the serial number all cases and bullets bills, the powder trace tag bills, primers that go bad after a few months/years bills, the UN ammo bans.
Hope this helps.