If it's raining, I would agree with those who are saying Victoria Line (Northern Line is a considerably longer walk and also involves more stairs) to Kings Cross then change to the Circle/H&C to Liverpool Street 


I don't understand the reference either. The station is situated underneath the Euston Road so there is no underpass to be used, just one of the two station entrances.
I want to avoid Euston Square, Northern or Vic and where to?
Euston to Moorgate via the Northern line is rather circuitous (the Circle between Euston Square and Moorgate is much straighter).