I feel it's about fairly even, with the Alliance getting the edge to win for me
Highmountain taurens are -just- Taurens with antlers and facepaint, and I dislike Taurens to begin with
Nightborne are essentially scuffed Night Elfs in my opinion
Mag'har Orcs are pretty okay though, love the fact that they can be costumized to resemble a member of any (almost?) Warlords orc clan
Zandalari trolls are pretty awesome I will admit that
I like Void Elfs, for me they're 'improved' versions of Blood elfs (more costimization options, love their passive turn-to-purple racial)
Lightbourne Draenei for some reason look a lot better than the regular Draenei for me, although I do find their heritage armor to be boring
Dark Iron Dwarves are awesome, their fiery beards, fiery eyes, head tattoos.. awesome!
Kul'Tiran are easily my favourite addition, I LOVE the Male Kul Tirans, they look awesome in plate and leather, imo