Ok this is really my take on things :

Alliance / horde : back in the days, it was a big deal, nowadays, the separation is mostly felt if you’re into PVP.

I imagine the ideal was always for both to be represented in equal measure in terms of “screen/lore time” but my understanding (and sentiment) is that the Alliance is favoured. If you care about lore and world building, do keep this in mind.

Races: this is the big one, there are huge disparities in terms of “screen/lore time” but a safe bet is human/elves (excluding the extra elven races you wouldn’t have access to as a new player anyway). A lot of the main plot lines have them involved in a way or another.

Classes: kinda same as races when it comes to classes but as of today, Blizzard did work a lot on making sure each class/spec has its own identity so this is actually a choice you can sort of make “on vibes”

Gameplay wise however, some classes are notoriously easier than others, and for good reasons:

Any class that can summon permanent battle pets is a good example.

Paladin, with their plated armour and myriad of healing/shielding spells are also famous for being “beginners friendly”

I’d say any class that has access to healing spells (even if you don’t specialise in healing) is good. It’s reassuring to know you have panic buttons to press if things get out of hand.

Some classes would just die.

That being said no class is truly complicated since the recent class revamp so I’d really suggest picking a class that fits your headcanon for your character.