Don't do the change at Hammersmith, unless you're familiar with the layout there. There's actually two stations there, and you have to leave one, cross the street and enter another. I actually quite like this route, but wouldn't recommend it unless you know the area.

Changing at Green Park gets a bad reputation, but there are elevators in the station now, and you are also able to do it using escalators (marginally faster) - just head towards the main exit, but then turn and go back down towards the Jubilee Line instead of passing the barrier.

Changing at Piccadilly Circus, you cannot avoid steps. It'll also be full of drunk people.

You won't get rush hour crowds, but weekend evening trains can get quite busy and lively. Not in a nasty way, but it's a world of difference from the near-silent carriages of commuter times. Consider it an introduction to London drinking culture...