For May there's kind of elements of each that I like, whereas for Brendan the old one wins hands down, mainly cause the art that's shown there is Emerald Brendan which is my all-time favourite Brendan lol xD This is due to outfit, hair colour, hat and eye colour.
With May, I like the outfit on both but perhaps more so on the new one; however, I think the hair + hair accessory combo on the old May just works so much better, it's like she was born to wear a bandana lol xD
A point I'd like to make about both old designs is that their addition of gloves + wristbands totally completes their outfits, which the new ones are sorely lacking imo.
Therefore, overall I'd go with the old designs as to me they're still two of the best-designed protagonists :)