My own personal preference for SD ammo is medium-to-heavy weight bullets. In 9mm that'd be 124-147gr. Lighter weight bullets don't tend to penetrate as deeply and for SD you want rounds that will penetrate deeply enough to reach vital organs, major blood vessels, etc., while minimizing the possibility of overpenetration.

I like Dr. Roberts' list of recommended ammo. His research involves not only gel results but also the results of actual shootings. He generally recommends against 115gr 9mm JHP because of the lack of penetration they tend to exhibit, with the Barnes all-copper bullet being the only exception the last time I read his list. If you choose a round from his list, I think you can be confident it'll serve you well. If you don't want to overthink things, which is probably a good idea, you could just Google his list and skip the rest of my novel post.

Regarding .357Sig vs. 9mm, service caliber rounds all perform similarly, whether in gel or actual shootings. A bigger or faster caliber may have a slight edge in performance, but I haven't seen anything to suggest it's a significant edge. I think the one area where .357Sig does seem to outperform other calibers is in hard barrier penetration and subsequent soft tissue/gel performance, so that may be something to consider, though I think that's more of a concern for LE.

My own choice for 9mm is the 147gr HST, which is what I keep in my HD gun, a Beretta 92FS. It performs well in gel, but I try not to rely solely on gel results; I prefer rounds that have a good track record in actual shootings. Massad Ayoob, who keeps tabs on how rounds in police service have performed in actual shootings, has said that agencies using the 147gr HST have been satisfied with its performance.

The one issue I have with the Lucky Gunner tests is that they don't use the same gel as the FBI when they established their standard. The Lucky Gunner results are ok to compare between rounds, but I would not use their results if I'm using the FBI standards as my frame of reference. If you're watching YouTubers testing ammo in gel, pay attention to what kind of gel they're using and what their frame of reference is. I can't remember their exact names, but IIRC tennesseeoutdoor9 and ShootingtheBull both use the FBI formulation, and both had good performance from 147gr HST.

One thing I've never understood is why posters bring up missing whenever the subject of overpenetration comes up. Missing the target is a concern regardless of the type of ammo you're using. But if you are able to get solid hits on target, the FMJ has a much higher likelihood of overpenetration than JHP (this is aside from JHP also having a much higher likelihood of causing more trauma than FMJ). When the NYPD adopted the 9mm they started with 115gr FMJ. They switched to JHP because they had too many instances of rounds going through their intended targets and injuring bystanders as well as other officers. While it is important to be sure not only of your target but what (or who) is behind your attacker, the stress of a life-threatening encounter can induce tunnel vision and make it difficult to do so. Or there may be a situation where you just have to take the shot because it'd be more dangerous not to (active shooter situations come to mind).

Having said all that, carry what you're comfortable with. As I mentioned at the start, service calibers all tend to perform the same, so choose the one you prefer. If you like .357Sig, pick a gun you like in .357Sig. If you're a .45ACP fan, carry that. As long as your gun/ammo combination is reliable and you can shoot it well, and you're willing to carry it, you should be well served.

Just my opinion.