Marshal isn't my favorite name, but I greatly prefer it over warlord.
It has a few advantages:
1) Doesn't imply high level power. No matter how you phrase it, warlords sound like high level characters to me.
2) Doesn't imply evil. I know there's a comic book character warlord and all of that, but most people think of evil usurping bad guys when they think of warlords.
3) Isn't almost identical to another class name. There is the problem with a Martial Marshal, but that's a minor problem compared to my buddy the warlord and my buddy the warlor...I mean warlock.
4) Its already in the culture. Not everyone has the MH, but many do, or at least have heard of the marshall from enworld, or just that one guy at the table that has every book in existance. Its an easier name to acculumate.