Board presence

[Tyr Anasazi]

The best kind, 0-cost ability, in theory works for ever as long as the card is still in play, e.g. Death Mage Thaddeus.

Next on the list, is high attack that is enough to one-hit kill or damage-based ability e.g. Raven Wildheart. Although there are exceptions such as Defender and Molten Destroyer.

Then it is resource-cost abilty, e.g. Plasma Behemoth, Jasmine Rosecult. They are not so good in early game when resource is scarce.

Worse than that is SE-only based ability. Because it is always 1 SE/turn unlese you pay card and resources for more SE.

After that is weapon/persistent or multiple turn ability. You pay 1 card and resource upfront, then pay 1 durability and maybe Hero HP every time you use the weapon, or simply get the benefit till the ability is removed from play.

Near the bottom is just attack, not enough to avoiding defending damage. You spend the HP of that ally, or even its very presence to use its attack.

Last on this list is one-turn ability, you pay 1 card plus resources to use its effect once.