I can only give anecdotal evidence on this. I prefer to walk on my treadmill desk which tends to have less impact on my knees and hips. Standing or sitting without motion will eventually tire me or cause some pain, though I generally find I'm likely to move around more while standing. Sitting for too long just tires me out.

I rotate through all 3 though throughout the day, so if my knees are bothering me or I feel like taking a break, I'll sit down for a bit.

The most important thing once I starting using the treadmill though was investing in decent shoes.