Unlike practice ammo, the best 9mm for self-defense is the ammo that you can trust is going to be effective, consistent, and reliable with every shot. For the best terminal ballistics, prefer Jacketed Hollow Point ammunition for any self-defense application.
When it comes down to it, the brand and type of ammo is extremely important. For self-defense ammo, most professionals prefer a heavier grain bullets for optimal performance. This is great for full size or even compact pistols, as the weight of the pistol can tame recoil. However, with sub compact and smaller guns, recoil is snappier already, and throwing in the added recoil of a heavier bullet can make it hard for fast follow up shots. Moving down to a 124gr hollow point might be the better option but of course it is heavily dependent on you and your gun.
Federal HST 9mm Jacketed Hollow Point ammo is one of the most popular options for self-defense ammo. The 147 grain 9mm hollow point ammo is designed to expand up to almost twice the original bullet diameter without breaking apart, maintaining 100% weight and not over penetrating. It is also barrier blind, meaning that it can penetrate heavier barriers like thick clothing without expanding until it hits soft tissue. The brass casing has also been Nickel plated to reduce friction and allow for more reliable extraction.
Another great 9mm round for self-defense is the Hornady Critical Duty FlexLock. This 9mm round features a hollow point design with a plastic insert in the hollow cavity. This plastic insert prevents the hollow cavity from clogging from clothing or other soft material. If a hollow point gets clogged, it acts like a standard round nose bullet, failing to expand properly in the target. The FlexLock insert improves consistency of expansion by pushing the wings open when impacting a fluid target.
Other popular hollow point rounds include Speer Gold Dot, Federal HydraShok, Winchester Defender, Hornady Critical Defense, and SIG V-Crown.
Moving away from JHPs, 9mm solid copper ammo has grown increasingly popular with offerings from Lehigh defense. These bullets come from solid blocks of copper and feature a unique fluted design that uses hydrostatic energy to create a large wound channel. This reduces the chance that barriers such as wallboard, sheet metal, glass, and thick clothing will damage the bullet before impact. Of course, more penetration can also be detrimental if you miss your target, especially if you live in an apartment complex or condo.
Like everything firearms related, bullet selection relies on your specific situation and use case.