IMO UF is the best box to get.
It has three *pokemon.
Blissey ex, Espeon ex, Feraligatr ex, Ho-Oh ex, Lugia ex, Meganium ex, Politoed ex, Scizor ex, Steelix ex, Typhlosion ex , Tyranitar ex, Umbreon ex
And you get three of the above pokemon. Lugia and steelix are two of the most valuable and popular exs, worth more than Blastoise, and Lugia is worth more than Charizard. It is DEFINITELY the best box.
Every one of those ex's is tradeable, and some, like blissey/scizor/lugia/steelix/espeon can get you a lot of trade value.
Let's not forget it has all the special energies, trainers like PETM, Protective Orb, and cool holos like Ariados, Typhlosion, Bellossom, Slowking, Houndoom, and Poygon2.
If you are going to be buying packs, buy UF hands down.