Nostalrius Begins - Quality wow vanilla realm (1.12)

hi ppl

i decieded to lvl one ofr them , both are 20 lvl...

My question is, which one is better / most utility for high raiding ( NO PVP )

priest: advantages / disadvantages?

shaman : advantages / disadvantages?

as I saw , mostly guilds need resto shaman, any specific reason?

thank you all for replies

greetings