What is the best caliber for self defense?

[Jerzees]

@Aaron25

Sunday is a 5.7 x 28 with 28 gr. polymer tips.

Could you please share your thoughts about polymer ammo on the thread linked below? There are few people who are interested in using it.
Thx

Synthetic Jacket Range Ammo

I found a decent deal on some FMJ 9mm that has a synthetic jacket. I remember reading that the synthetic material can build up in the barrel and cause fouling. Has anybody used such ammo and if so, did it cause any problems?