Gunlearn, if I take it correctly that you are from Ecuador, Welcome to the "TFF Foreign Legion!" We are proud to have distinguished members from El Salvador, Brasil, the Phillippines, Australia, Canada, Eastern Europe, just about everywhere! We love 'em all, and they teach us "Norte Americanos" a lot too!
Having said that, being limited to 10 rounds, I HOPE you can carry "real" calibers, not like some latin American countries that limit civilian use to "non-military" (i.e., NOT .45 ACP) ones.
What caliber are you using?
If LESS than, maybe a .40 S&W, the only advice I would say is stick to something with good penetration, like FMJs if there are car bodies in the way, and PRACTICE PRACTICE PRACTICE "head shots....." until you can consistantly hit them at about 7 yds or less QUICKLY from a draw, and up to 10-15 yds, with a GOOD gun and technique maybe even 25yds with a little, (VERY little!) more time....
But if you are LIMITED in rounds, then opt for the LARGEST caliber you can own in an autoloader.
Just another thought...
Does that stupid law apply to revolvers too? Or are they just trying to "discourage' autoloaders? And can you carry LOOSE spare ammo, if only "one mag", can you maybe carry a revolver speedloader, or maybe a drop pouch or "speed strip?"
If there's a way around it with a revolver, and they let you carry more LOOSE rounds, you MIGHT be better off with a .357 mag, because even loose rounds would load in a revolver slowly, but MUCH faster and easier than reloading your one single auto mag!
Plus your scenario dealing with cars, that was the claim to fame for the .357 in it's heyday here as an LEO gun, in fact why a model was NAMED the "Highway Patrolman...."...better penetration of car bodies!
And finally, while I would NEVER advocate doing anything illegal
, we have an old saying here:
"It's better to be tried by 12 (a jury) than carried by 6. (pallbearers at your funeral.)
Is there a way you could "hide' an extra mag in your back pocket next to your wallet, or in your sock or somewhere "just in case?" It might be worth the risk if you are talking life or death from the 'bad guys," who by definition obviously don't care about any law!