I need to get between King’s Cross and Waterloo Main line stations a week on Friday (2nd September), arriving at Kings Cross around 1pm.

There seem to be two options:
Taking the Piccadilly Line to Leicester Square and then changing to the Northern line
OR
taking the Victoria Line to Euston and changing onto the Northern Line there.

Which is the better route?

What means "better"?

TFL says neither: Victoria to Oxford Cir; Bakerloo to Waterloo.

Now, I don't know why TFL says what it did, and the native Londoners will know better. But the usual reason is ease of transfer - the Piccadilly-Northern connection at Leicester Square involves a bit of running around, as may the Victoria-Northern connection at Euston.

It's 10 minutes walk to Euston from KX

By better I mean which is the easiest - thinking of escallators, crowds, convenience of cross platform transfers and things like that. I suppose what I'm really asking is which route would a Londoner use? I'll have a small suitcase, back pack and walking stick. I'd looked at walking from KX to Euston, but had discounted it.

I'm thinking that TFL has taken your concerns into account, and that is why the routing that seems more direct on a map (read: the two options you asked about) was not selected.

So Oxford Circus it is.... Thank you for your help.

> It's 10 minutes walk to Euston from KX

Ewwww, walking.

If memory serves (I think there was also a thread on this here, years ago), the Victoria-Bakerloo exchange at Oxford Circus is all on a level through a fairly short passageway.

Thank you Patrick, that is the kind of information I want to know.