There’s nothing like starter MG, since all of them are at least BR2.
But I like the Japanese Type 11 most. Especially because of its unique reload system. You can use up all your ammo effectively. Which is very important for new players. Since they can’t have bug ammo bags yet.
You should elaborate what do you mean by starter smg.
Starter as the first weapon in it’s class in the tree?
For best first LMG I would say Breda 30, maybe I’m just biased since I used that weapon a lot pre-merge.
Best SMG is the Japanese S-100 SMG obviously.
For smg I would say URSS with PPD 34 that have a massive rate of fire or the american with the sten gun with his big mag for his br and his recoil is easy to control