If i had to choose one it would be a 4v4 map because it would get more playtime, however if I chose a BTB map it's either be Headlong, Sandtrap or Breakpoint.
For 4v4 it's a toss up between The Pit, Beaver Creek, Damnation, Zealot and Countdown. I'll choose The Pit, very versatile map that gets hype.
There's a lot of maps in Halo that could do with a re-imagining though. I always felt Reach was so close yet so far. Boardwalk, Powerhouse, Swordbase and Reflection all were close but needed some alterations to flow better. Even Condemned, though that would need a complete overhaul, like remove the middle and make it chillout-esque, the aesthetic was cool though. H3 had some great mid-sized maps that could be reworked like Highground, Longshore & ghost town. If Halo takes a leaf out of overwatch's book and uses territories like a phase then those maps could get a lot of use. H2 had some great BTB maps like Terminal and Waterworks etc.
I wouldn't like to see many remakes in the new game but i would like to see 343 using winning or promising layouts and using it as a springboard, because i don't see much promise in their maps imo. I liked Plaza, though the colour filter on it made it hard on the eyes.