So I flew on VA1 a few days ago...
Row 20 is excellent for knee room, not so much for leg extension. Unlike row 3 on the 738s and E90s, there is no cut out at the bottom of the bulkhead.
I'm 180cm/6' and I could not stretch out fully, whereas I find row 3 gives me effectively unlimited leg room. Row 20 gets two full windows and a view into a third, which is sweet. 20D/E/F seems to have a bit less leg room to start with, though I didn't measure or test sit. 20C/H don't have this problem though, as the bulkhead wall is only about two seats wide and it is actually the aisle in to premium economy directly ahead of you, with unlimited legroom. Being bumped is not an issue as no passengers should be moving forward/backward at this point, there only being a curtain in front of you and no lavatories.
Conclusion: 20A/B/J/K can be quite comfortable for a couple who don't mind sitting diagonally to share the leg room, with some criss-crossing of legs, and I would pick it again over any other non-exit row. For a solo traveller though, 20C/H is really what you want.