I wear Centurion armor because, well, it has more of a resemblance to Chief's armor in the campaign. Plus, it seems more spartan like compared to some of the other ones. I also wear the Decimator helmet 'cause it resemble's Noble Six's MKV[b] variant that I used often back in Reach. It feels unique to me with the combo that I have right now.
As for the visor, I've been a little undecided for a while, until I settled for the Dianthus. I guess I like the visor with a bit of the purple-ish color to it. If you look at it one way, you can see it has a close resemblance to the traditional spartan visor, but with a different twist to it. It also looks good with the black armor I'm wearing.