The bigger question is what class are you travelling and are you seeking to upgrade (and now when, if it is beyond April 2011 things will be different).

Assuming pre April 2011:

In economy, the 747 is arguably preferable to the 777 because of greater seat pitch (34 vs 32 though the seats themselves vary somewhat).

In premium economy, the 747 is definitely preferable to the 777, as the side cabin on the 747 in front of economy (and upstairs) are both preferable to the 777 3-3-3 configuration. 747 seating is slightly wider, but the cabins are far more personal.

In business premier you're fine both ways, but the 747 has the nose cabin which is preferable to the 777, upstairs arguably is better too.

In all cases if you are seeking to upgrade from economy to premium economy you probably have a better chance via HKG, but it is marginal as 747 and 777 cabins have similar sized premium economy cabins. Going to business premier you'll have a better chance on the 747 as there are 26 on the 777 and 46 on the 747. I'd choose via LAX because of the hard product and because I have transited LAX many many times so it is tolerable. However, HKG is always an easier transit.

After April 2011 there is the new 77W product via LAX which means new seating in all classes on that route compared to HKG until the 777-300ERs get refitted with the new product.

However. If you are in economy travelling alone you get 10 abreast seating via LAX vs 9 abreast via HKG on aircraft with the same width. You can buy Skycouch via LAX but not HKG. The new premium economy via LAX will be well ahead of the product via HKG. Business Premier hard product will have small difference, soft product probably better through LAX.

Um so good choosing!