Char is more like Erwin Rommel, then Ramba Ral was.
Fact is Char was the first, true great ace pilot of the new weapons know as tanks, er I mean mobile suites. Just like the real life Desert Fox, he was latter outdone by a man who looked up to him, at least in some form.
Zechs Merquise is more akin to a traveling Knight of old, he does good, he does bad, but all he justifies by his code of Chivalry, even if his own take on chivalry is not so chivalrous. In the latter half, he is more akin to a last Crusader, willing to go to any lengths to get back the dream that was Jerusalem/Sanc Kingdom, even if that means utterly destroying it in the process, and so going against the message that was Jerusalem/Sanc Kingdom(goodwill and peace to all men).
Anyway, between the two, Id give it to Zechs, Char while awesome, is outdone so much by other pilots, where Zechs, in a mobile suite thats not even made from super duper gundaium(save for the epyon arch) takes on better suits, and comes out on top, or at least alive, which is more then can be said for other aces.