KEEP IN MIND This is using the original games, so ruby and sapphire not emerald.
Team rocket grunts, which are the brunt of the team (pun intended), use poison types the most, however because of the sheer amount of rattatta, normal types are second place.
Team aqua uses Dark types, Water types and poison types. I would say they use dark types the most, because they use many poochyenas, and all of their water types (or most of them) are carvanahas, which are dark types, so I would say that they are mostly using dark types.
Team magma uses Fire and ground types by a SLIM majority. One, in fact. They use numels
Team galactic uses poison types the most, because of their uses of stunky, zubat, golbat, croagunk and dustox frequently.
Team plasma tends to use dark types, because of their high frequency of Scraggies, sandiles, purrloins and their evolutions.
Team Flare tends to use poison types, because of gulpins, zubats, croagunks and their evolutions.
Team skull also uses poison types, and has a wide variety of them in fact.
Team Rainbow rocket, being an evolution of team rocket, still uses the same mons. So poison again.
The Aether Foundation uses a tie I believe of flying and normal.
Finally, I say that there are 2 "evil teams" in sword and shield. Team yell really isn't, but it's counted by one, so I'll do it, but no one mentions the macro cosmos, who I would say are more evil. I'll put both.
The macro Cosmos use steel types primarily.
Finally, the team team yell uses dark types.
Hope this helped!