Batman and Wonder Woman for me.
Batman, for finally getting a suit I waited for years to see. And all that attention to detail, like those scratches on the batsymbol, etc. really surprised me.
Wonder Woman, because I didn't know what to expect and Wilkinson managed to make it to visually stay true to the comic book look while still seeming practical enough for live action and making sense on its own. There are some things I would tinker a bit, but overall, it was probably a toughest costume to tackle and the execution is great.
I must say that I like Superman's costume a lot, actually, it is probably the most beautiful suit among all those costumes. But, while definitely better looking than MOS suit, I already knew what to expect when it comes to his look.
Same goes for Lex. I knew what to expect. Eisenberg looks good, but he looks exactly as I thought he will.
As for Aquaman, the suit is growing on me, but it initially left me underwhelmed and I still think they could have done a better job. Momoa looks good though.