The CorBon round was arguably the king of the 9mm SD rounds back in its day, but there are a few better rounds these days. Bullet technology has come so far in recent years, but CorBon still uses non-bonded Sierra bullets (assuming you're not talking about the DPX loads, since you didn't specify it). There are definitely far worse choices than the CorBon, but the non-bonded bullet can still fragment, and penetration is on the lower end of what's desirable.
My vote is for Speer 124-gr. Gold Dot +P. The bonded bullet doesn't fragment, and penetration is just about ideal. The delta in muzzle velocity between different cartridges is also among the lowest in the industry, indicating a very consistent and high-quality manufacturing process; some other company's rounds can show pretty wild swings in MV from cartridge to cartridge. I also find the Gold Dot to be a soft-shooting round. I can't really tell the difference between it and FMJ target ammo, even in a small 9mm like the Walther PPS. That's definitely not the case with the CorBon. I'm a bit of a recoil junkie at the range, but in a self-defense situation, the CorBon's extra recoil just means slower follow-up shots with a less effective round.
Anyway, the CorBon is still a very effective SD round. It's just that there are a few better ones today.