Where do I begin?
I am a big fan of the .380 round and have been carrying one type of gun or another in that caliber, daily, for as long as I have had a permit to carry. Lots of opinions and speculation in this thread, I would just like to tell you what I KNOW. I KNOW that the 102 grain Golden Saber bullet is capable of expanding reliably when fired from a Kel-Tec, to a diameter of 630 digitally measured thousandths of an inch. They dont always expand reliably, especially when they strike at an angle. But they do stay bonded and until the Hornady Critical Defense came along they were my #1 choice, a close second was the Winchester Silver Tip (no longer in production in .380) they expanded to 590 thousandths of an inch, again, not always reliably.
There are lots of good choices out there, but it was not lost on me that this thread is titled "best .380 BULLET" rather than best .380 ammo, that being said, it is worth noting that Double Tap uses the 102 grain .380 Golden Saber bullet in the production of thier defensive ammo, which is produced to "high" velocities. Good choices for .380 ammo also include, as mentioned by a previous poster, the new Winchester SXT, which is just a reincarnated (and improved) version of the famous Black Talon.
The problem with rounds like the Corbon and Federal HST is that thier flat bullet profile is not always conducive to reliable feeding in many of the "pocket" .380s now on the market, then there are others like the Remington 90 grain hollowpoint that almost always result in the separation of the bullet from the jacket when fired into pretty much anything other than paper targets, or the Wolf "Gold Series" hollowpoint that doesnt even have enough power to knock down a steel plate target at a distance of 12 yards that a standard 95 grain bullet from pretty much any other manufacturer could do easily. Its a slippery slope when you are trusting your life to a .380, choose wisely.