Best train to Kolkata ( hwh as well as koaa) from smi; raxual; dbg, mfp. In your prospective
1)rxl -hwh exp: from raxual
2) mithilanchal exp: from sitamarhi
3) smi - Kolkata exp: from sitamarhi
4)gangasagar...
more... Express: from darbhanga
5) Mithila Express: from raxual