Well let's see, I'm quite partial to the OYW stuff so my choice would basically be sort of a re-telling of that.
Changes I can think of off the top of my head:
-MSs are scaled down, they become fancified, bigass suits of power armor, rather than the archetypal 'real robot' common in the show. (granted, that sort of totally shits all over one of the rules in this thread, but I think it would work) MS pilots/MS battles still tend to be the focus of the series, but they are shown to be only one aspect of the overall conflict.
-More spaceship battles! If I remember correctly, Gundam series tend to have a problem where they have a bunch of spaceships that never really do anything (or no spaceships at all which end up being kind of weird, like Wing); with mobile suits altered to *not* be the be all end all of combat weaponry, there is now room for spacecraft to fight each other, even if it is in the background while the brave squad of commando MS pilots fights to destroy the enemy orbital supply base.
-I'd try to keep things *looking* hand drawn. I'd be fine with cg when it was blended into the show well enough, but I'd prefer that the show looked more like
this than
this. (granted, Macross F isn't trying to be particularly serious, but still, other shows that have had more of a pretense to seriousness have used a similar animation style, and the whole sense I get of the animators just thinking "ooh, wouldn't it be cool if we did this?!" and nothing else just rubs me the wrong way)
-Probably have the show as a 13-26 episode OAV. Each episode would more or less be a short story following one of several groups of people involved in the war. (e.g. the group of colony dwellers forced from their homes, the ace MS pilots who keep ending up at the same battle, the lovably inept group of cadets who narrowly survive each of the big battles)
-Background is pretty similar to the original UC stuff (Zeon vs. EF ect.), but with the scope expanded a bit (Mars, the belt and Jupiter are more directly involved, in fact, I think Mars or the belt would be a better location for Zeon's seat of power during the war).