you can name ANY map from all Halo games 
Halo: CE - Prisoner, due to it being the first map I ever played in the whole series.
Postnote: I never got to play on the PC maps, but Timberland, Infinity, and Gephyryopthing looked cool when trying them out solo. Will have to wait for the MCC to evaluate them properly.
Halo 2 - Terminal and Colossus most likely.
Halo 3 - Guardian, High Ground, Last Resort, and Sandtrap
Halo 4 - Perdition and Haven
Halo Reach - Boneyard and Forge World
Halo CEA - Prisoner & Timberland remakes
Colossus and Terminal, Halo 2
Spire from Reach. A remake needs to happen.
I love Spire and Countdown from Reach!
Blood Gulch
I was only able to play some of the Halo 3 DLC maps once but I had a blast on Assembly and Citadel. Also Blood Gulch, it’s a classic.
Halo 1: Danger Canyon, Death Island, Timberland & Boarding Action
Halo 2: Containment, Backwash, Terminal, Zanzibar, Desolation, Relic, Turf, Waterworks & Gemini
Halo 3: Sandbox, Standoff, Orbital, Avalanche & Rats Nest
Halo Reach: Highlands, Spire, Breakpoint, Tempest, Sword Base & Boneyard
Any map with city architecture are always my favorite. Boardwalk, Skyline, etc.
Boneyard
Boneyard
Blood Gulch and Hang 'Em High.
I have sooo many ahhhhh …
Guardian from Halo 3
Halo 2 - Lockout
Halo 3 - Standoff
Halo: Reach - Reflection
The Pit! 
Haven is my favorite map because it’s so beautiful and easy to play on.
Vahala is also a great map.
Guardian.
These are all my favorite maps, (what for) on the right. Map title on the left. Game up top.
Halo 3:
SandBox - Creating
ThePit - Slayer
Avalanche - Slayer
Halo Reach:
Forge World - Creating
Spire - BTB
SwordBase - SWAT
Penance - Anniversary
UnEarthed - Firefight
Halo 4:
Haven - Slayer
Adrift - SWAT
Ragnarok - BTB
Impact - Creating
Shatter - DLC
Halo Wars:
Barrens - 1v1
The Docks - 2v2
Terminal Moraine - 2v2
Glacial Ravine - 3v3
Fort Deen - 3v3
Halo 3 ODST:
Chasm Ten - Firefight
Crater - Firefight
Winward - Firefight