Turn A Gundam is the best hands-down.
Tomino brings humanity back to an age of innocence. The curiosity and wonder with which the characters explore the possibilities of the "Lost Technology" is as beautiful as the child-like terror with which they regard the tragic events of the "Dark History." The simple fact that there was only two Gundams in the entire series, and that the weapons systems werent fully understood until the end is impressive. Tomino was able to tell a story without gorey overkill / spam-killing (
I'm looking at you Gundam SEED
)
The concept of the Dark History unifies all of the various Gundam Series by arranging them as different periods in humanity's past, and the homage paid to each of those series is tasteful and not overdone for glitz or glamour. Such as the main bad guy, Gym Ghingnham, being a decendant of Uso Evin from Victory Gundam, who was himself decended from a love-child of Nanai Miguel and Char Aznable; the main bad guy of all that is Gundam. Gundam Wing found a more direct heir in Corporal Corin Nander, who apparently experienced the horrorific power of the Wing Zero Gundam before being put into cryogenic suspended animation for 'bad behavior.' Countless other references bring all the series together in the viewer's mind, stirring up memories of all the series simultaneously, enabling the finale to conclude the entire Gundam Universe. All true fans of Gundam who have watched all of the other series should know what I am saying, and should understand how good it feels to have
everything settled, once and for all. That the purpose of the Gundam, bringing peace, finally made good on its promise.
Turn A Gundam...is definitely the best.