Upstairs on the 747 is Club World only, not First. If you've never done it and 747 CW is available on your chosen route, I wouldn't rule it out in place of F. You could even do CW be way and F the other.
There's more space in F on the 777 than the 747, but the 747 feels a little more exclusive in the nose of the 747 than in the 777 which tends to have more foot traffic.
Another factor to consider is the route and whether your 747 is guaranteed to have New First. All the 777s now have NF, but some of the midJ 747s still have the more dated Old First product. With the latter though, you'd be eligible for 50,000 Avios per person compensation.....