Nothing rivals LAX
in number of movements, also lots of flights there, not too cold and great places to spot from.
Even if you don't have a car, you can go to In-N-Out Burger on the northern side of the field which is maybe a ten minute walk from Terminal 1. You'll be able to see everything landing and taking off on the two northern runways.
You can also take the bus to the C lot and from there the bus to El Segundo and the Imperial Hill, where you will have a great view of the southern part of the airport and with a telescope you can probably read off things off taxing on the northern part of the airport too. The Imperial Hill has great parkbenches where you can sit and just a five minute walk westwards are 7 eleven and other stores where you can get refreshments. You'll probably go away with 200-300 new numbers after spotting a full day if not more. I usually alternate bewteen the two places when I'm there.
Boeing 777s flown: UA, TG, KE, BA, CX, NH, JD, JL, CZ, SQ, EK, NG, CO, AF, SV, KU, DL, AA, MH, OZ, CA, MS, SU, LY, RG, PE, AZ, KL, VN, PK, EY, NZ, AM, BR, AC, DT, UU, OS, AI, 9W, KQ, QR, VA, JJ, ET, TK, PR, BG, T5, CI, MU and LX.. Further to fly.. LH 777