Mostly welcome or Mostly welcomed?

[skydown13]

A: Thank you!
B: You are mostly welcomed, You are most welcomed, You are most welcome or You are mostly welcome?

Which is the correct form?

 

[Rover_KE]

Please tell us first what your choice would be.

 

[LVRBC]

...most welcome.

 

[Rover_KE]

Please tell us first what your choice would be.

Never mind, then.