can you help me which sith raid teams to go for?

If you're working towards heroic STR then you should be farming death trooper to 7* as well as nightsisters. Thrawn and Imperial troopers are a good p2 team along with phoenix.

The 4 teams you should focus on:

JTR (with BB8, R2, RT and Rey Scav)
Jedi (GMY, HY, Ezra +2).
ChexMix (CLS, Zolo, DT, Chirrut and Pao)
NS (zAssaj lead, Daka, zombie, Talia and MT/acolyt).

Several other teams do decent, but generaly less damage than the above.

yeah, I am starting with Jtr and chex mix

you could also work on getting Sabine up to 7 stars and then gearing up your Phoenix squad. not only are they good in P2 (with the requisite Zetas) but they’re one of the most versatile teams across the entire game