Please explain, how do you mean build order?
About heroes, I like Firelord mostly, but if I need to chose in races directly, I am using death knight. Banshee is also cool.
Firelord has my favorite spell, soul burn, then Lava spawn is used as additional unit, Incernate is used to add damage, and Volcano in enemy's base.
When play with Death Knight, I am using him to support my units or damage enemis with death coil.His Aura is awesome for speed and regeneration, when Skeletons are away, I am using them to convert their HP to heal death knight, and Animate dead is awesome for bases.
Banshee, well her Silence is useful to prevent enemis from casting spells, Arrows are good as additional damage and create skeletons, Life drain can be used to heal herself and damage enemy, and charm of course is awesome ability