Best: X1 Armor, Force Armor, 'Neutral' Armor
X1's armor, while being the first and simplest, also got the job done. Simple as that.
Force Armor was great because of the two bits of customising with the busters. It was a good design as well.
Neutral took all that.. And ramped it up to what.. 3 Different Armors? Icarus, Hermes and Ultimate. I absolutely love the customisation of this armor and its look. Plus the Ultimate armor glows purple. [tornado fang] yes. The game may've sucked but the armor was kick ass.
Almost Had It: Max Armor (X3)
This armor had so much [parasitic bomb] you could do with it. Once you upped it to gold, its was a nearly unstoppable force.. Only nearly because of how incredibly bad the buster was.
Decent Armors: Falcon Armor, X2 Armor
Self explanatory.
Meh Armors: Gaia Armor, Blade Armor
Again, self explanatory.
[parasitic bomb] Armors: Glyde Armor
USELESS
Undecided: Shadow Armor
I didn't like the Gaia Armor because of it taking nearly everything away. I don't like the Shadow Armor's buster. I'd be able to make more of a call if X6 was so incredibly [parasitic bomb].
Honorable Mentions: Limited Armor (Megamissions 1), EX Armor (Megamission 2), All X Armor (Megamissions 3)
Say what you will about its canon status, but the Megamissions series had some kick ass variations on armors and I really love the way they look.