As far as trying to figure out which way takes up more or less energy, it seems to me that it depends on the technique used and also how tired a rider is during that climb.

There's got to be some tipping point but who is going to try to measure that!

What I do observe is how those mountain stage attacks occur. The rider tries to break away and the others try to respond. If it goes as planned, the front rider puts it all out there off the saddle. Then sits down and repeats that cycle maybe two more times to shake off any responses.

It ends up to be the rider with the fresher legs.