I'm using http://www.heartharena.com/tierlist to help me with Arena drafts, and some of its recommendations don't make much sense to me.
I got the option for paladin (yay!).
One of my options is between ancient shade, abomination, and cobalt guardian.
The one that looks the best to me is Cobalt guardian. The tier list says it's bad, abomination is below average, and ancient shade is average.
Abomination would be great except that it damages yourself and your minions along with everything else. Ancient Shade great stats for its cost but does (a probable) 7 damage to yourself. Are these cards really good enough to be worth it despite their drawbacks?
Also, it ranks holy light as terrible. Why?
I'm thinking the tier list might do me more good if I know the reasoning behind the rankings.
It sounds like you value life too much. The core tenet of Hearthstone (and MtG for that matter) is that life is a resource you can spend to either get more card advantage or more tempo. The closer you are to death, the more life matters, but at the start of the game everyone has tons of life.
(Edit: The Dominion analogy of this is somebody who buys Estates and Duchies early because they give VP, and the winner is the person with the most VP. Meanwhile, that person who's willing to trash their starting Estates is going to beat them hands down.)
Cobalt Guardian is a 6/3 for 5 mana. 3 health is really small. Almost everyone will be playing a 3/2 for 2 mana, and several classes have spells that deal 3 damage from the hand. It's lots of damage if it lives, but in most cases it won't. The most often scenario is that you trade down, spending more mana than your opponent to lose 1 card each. The Mech synergy isn't good enough to justify stats that are so bad.
The idea behind Abomination is that you play it when you have 0 or 1 creatures out. If you have lots of minions, you don't play Abomination. So, the drawback is only a drawback in some situations. This is why Hellfire is a good card - you only play Hellfire when your opponent has more stuff than you do, making the trade better for you. Taking 2 damage is a great deal if you can get rid of several of your opponent's minions. What makes Abomination iffy is that it's only good to play when you're losing, making it bad if the board is even. The best cards are good to play when you're losing or winning.
Ancient Shade is a 7/4 for 4 mana. 4 health is actually a lot more than 3 health - it's much harder for most classes to do 4 damage. There aren't a lot of 4/3 minions for 3 mana, so usually your opponent has to use a 4 mana minion to kill it. And Ancient Shade will kill most minions that try to attack into it. You call the 7 damage to yourself probable, but it isn't. Think of it this way - how often do your games go to 10 mana for both players? At 10 turns, your odds of taking 7 damage are around 1/2 at most, and probably smaller. The drawback hurts, but it's not as likely as you think. (If Ancient Shade lives, you might be able to end the game before that drawback matters.)
Holy Light is bad because again, it only heals you. It doesn't improve your board, it doesn't remove enemy minions. All it does is spend a card to let you lose slower. Usually it's better to spend cards that let you win faster.