I might say Warforged Fighters are classified as the definition of customizable, as their features all make it as straightforward as possible to turn them into the best killing equipment.

Battle Master – Battle Masters use martial techniques to earn battles, seeing combat as

They’re also on a brief-rest recharge, in order to sense free to rely on them pretty normally. Both of those spells are extremely valuable, and in many cases in most casting classes, having these as bonus spells that don’t use your spell slots is priceless. 

EDIT: