These are the four traditional Catholic orders that I know exist.
This is my best understanding
correct me if I'm wrong
The FSSP(330 Priests) is probably the largest in America in terms of where you can get to for a Latn Mass, as some of their parishes share with the novus ordo. The FSSP is in communion with Rome. The work under a Novus Ordo bishop. Bishops own the deed to the Church. They encourage tradition but will agree to the new beliefs e.g. will encourage abstinence and fasting on every Friday but if you want to go by the new Novus ordo rules, that's okay.
https://en.wikipedia.org/wiki/Priestly_Fraternity_of_Saint_Peter
https://www.youtube.com/channel/UCMfKHm3IFmiIj_fr1dsUfsA
The SSPX(680 Priests) is largest world wide. Both the SSPV and FSSP are split offs of the SSPX founded by Archbishop Lefvere
https://en.wikipedia.org/wiki/Society_of_Saint_Pius_X
https://www.youtube.com/channel/UCTvY1fvpD7jnT-uKEyuTSaw
SSPV(not sure how many) split from the SSPX. IMHO, their theology is not wrong. They are open to the possibility of sedevancanism. I particularly like Father Jenkins.
https://en.wikipedia.org/wiki/Society_of_Saint_Pius_V
https://www.youtube.com/channel/UC7qx5iw1K0deq6cw1g6uWAA
ICKSP(200 members) Don't know much about them.
https://en.wikipedia.org/wiki/Institute_of_Christ_the_King_Sovereign_Priest
There's also Latin Mass said by Novus Ordo priest. Father Altman is rather famous for speaking out for the traditional Church. He's the priest who did the "You can't be Catholic and vote Democrat" speech.
Which one do you go to, and why?