In the future, I would recommend asking this in the 777 Seating thread.

Personally, I would go with row 21. While row 30 has a ton of legroom, people tend to gather there to stretch, and it is near the galley and lavatories, so there is a lot of noise and light. Row 21, OTOH, has a ton of legroom, and has no major disturbances.

BTW, if you can find someone willing to give you an SWU, you could upgrade with a W fare.