Payday 2 main weapon - what do you like and can recommend?

Best weapon is stealth. Sadly, people seem to think wearing masks is normal behaviour.

locomotive and sniper, cause damage damage damage

CAR-4 when fully modified is frankly one of the best Assault Rifles in the game. Although honestly it depends on what type of Heist it is.
I find myself using the IZHMA 12G and Locomotive 12G a lot. Locomotive 12G frankly has to be one if not the best secondary weapons you can get in game. In fact I would go so far to say that the Locomotive 12G is really my main weapon most of the time.

If you have the Sniper DLC, Rattlesnake or R93. Especially since they go through shields.

Well.. Heavy Eagle + Loco = Ultimate carnage. Though you can't 'conceal' the Heavy Eagle at all, 60 damage with the funnel of fun only.
Also if you are an enforcer, Consider investing in the perk that allows you 2 ammo bags, As for non-DLC, CAR-4 is your way to go, It can be concealed easily too.

silenced shotgun and ove9000 saw

Brenner all the way. Kill like shotguns but with more fun.

Locomotive Shotgun.

Just go Loco, baby.

Reinfeld + Loco

I am enforcer so my primary is a saw but secondary as others have said is teh LOCO

AK 762, Saw, Car-4 or Thanatos for primary and Loco for secondary. If I'm running Mastermind pistol build then it'll be Signature .40 or Bronco.

For me, the best Thanatos - barret, i'm a loud man.