I <3 Halo:Reach - amazingly fun and best campaign + amazing Soundtrack
I <3 Halo 3:ODST - best soundtrack + Firefight + Coastal Highway and Mombassa Streets, amazingly unique campaign.
I <3 Halo 3 - best multiplayer levels + Forge + best Custom Games + soundtrack
I <3 Halo 2 - amazing huge fun campaign + soundtrack + Fun multiplayer
I <3 Halo: CE - started it all
I'll try to give you the best answer.
If you buy Halo: Anniversary, the disc will come with the 7 Multiplayer maps for Halo:Reach. The game will also come with a 2 day xbox live code, AND a download for the Anniversary map pack. You can use either.
AND on November 15th, the Anniversary map pack will be out, and you can buy it for 1200 points on Xbox LIVE. It comes with the 7 multiplayer maps and nothing else.