Classical Greco-Roman wrestling, sistema and lethwei are most practical in my opinion for the average person. The highest form of martial art only suitable for people that would dedicate their life to training and especially fitting for SS since we already practice some of the inner techniques is Tai Chi.
Streetfighting brings invaluable experience to people that had the misfortune to be frequently engaged in physical confrontation situations and it cannot be replaced by any martial art. A huge part of these things is psychological so a strong body coupled with a strong mind can be quite effective.
It depends what your goal is. Self defence, becoming an accomplished martial artist or something else entirely.
SWP
Regarding wrestling vs other forms of standup martial arts, I will say this much:
Pit any Muay Thai fighter with a decade of experience against any professional wrestler with a decade of experience in BJJ, Judo and Grappling, and 9/10 times at minimum the wrestler will be one sidedly destroyed without even touching the stand up fighter.
In MMA almost all the most effective takedown defenses from the Muay Thai system are banned, in general in sport fighting almost all the most effective techniques are banned, because they are very lethal and in earlier times with less rules frequently resulted in broken necks and other severe injuries.
Since these athletes are fighting for sports, not for life or death, such extreme techniques are to the detriment of athletes, therefore sports fighting is not a good measure of how well you can use it to defend yourself.
Another thing to think about is the floor.
Outside, the floor is anything between asphalt or concrete to grass. All are harder than an MMA mat that is designed to dampen blows and prevent injuries from being thrown on the ground.
There is also the cage itself, which you can lean into and can be used as part of an effective defense, or the ropes in a Muay Thai or boxing ring. Which does not translate to being pinned against a hard stone wall in an alley.
Unfortunately not much that you learn as a sports fighter translates to reality.
What does translate is the athleticism you build, the toughness and perseverance, and the skill that surpasses an untrained person so you know at least a little what you are doing rather than not, and are athletic enough to escape a bad situation, be it though overpowering someone or through running out of there.
Tai Chi is not a martial art. I am sorry, but Tai Chi, in none of its forms will teach you how to protect yourself in a situation where your life is threatened.
I have seen many cases where this is taught, and it is always the biggest clown joke. I feel sorry for those who learn something thinking it will make them superhuman, when it in reality doesn't help them at all when they need it to save their life.
Tai Chi is amazing for its other benefits however, but it is not a martial art, same as Yoga is not a martial art either.
Sistema is unique, from what I have seen with my very limited exposure to it, the best thing it teaches you, better than most other systems, is how to remain calm in bad situations, keep collected under pressure and get comfortable being uncomfortable, which can be very valuable.
It does not do a lot of standup fighting though, so if you want to learn how to hold your ground on your two feet, one of the most important skills you can learn when it comes to defending your life, you are better of learning something that teaches you that.