I like them all except green (nothing against it, just that it's plain to me and didn't originate from the actual series like the others).
If I had a top three, though, it would be:
-1. Varia Suit: It's just classic, and plus, I've taken a liking to the more "gold" tone that the colors of the armor have taken on. I also think it stands out a bit more nowadays since everyone on For Glory and such all use the others.
-2. Light Suit: What can I say? It looks very good on the Other M suit's "upgraded for Sm4sh" look. It's always been my favorite suit after the Varia Suit anyways, so it's only fitting. The Light Suit is just such a cool, unique suit.
-3. Dark Samus: For one, Dark Samus wasn't playable, so part of me using this is to make up for that, but also, the colors just look so good and give a nice little intimidating vibe, though not quite in the same vein as the Dark Suit palette. Aside from that, it just looks so cool!
Honorable mention - Gravity Suit: It just looks so good in this game! The dark purple just looks so pretty, and I always like the blue visor for alternative purposes. It melded with the transition to HD perfectly to me!
... Also, Dark Suit: I used to use it as one of my main palettes to sport in Brawl, so I felt it was enough to warrant a mention. Dark Samus and Light Suit palettes surpassed it, though.