That depends do you have any dlc if not and you have money you should get the Mcshay weapon pack 4 it comes with a good Lmg with a built in flamethrower attachment and was the first pack I personally got but if not you should be diverse https://store.steampowered.com/app/2353510/PAYDAY_2_McShay_Weapon_Pack_4

PAYDAY 2: McShay Weapon Pack 4 on Steam@steam