ToME: the Tales of Maj'Eyal

Is lichform good or is it just better to be a skeleton if you want to play an undead?

Lichform gives +10 max resists, this lets you be extremely tanky if your gear permits this.

it depents on what racials you want though.

Also you don't need to breathe, you will not die from water and sand.
And lich is so fancy, after all.