What is the best way to get legendary cards?

I was disenchanting lately and realized there is no good way to get good cards to disenchant to get the legendaries. Should I get card packs or is there a better way to get cards?

You just have to buy lots of card packs and hope you get lucky.

This is why there's a purchase with real money option. They make it hard to get so people get frustrated and buy it with real money to speed up the process. The good thing I guess about hearthstone is that if you just play long enough you will eventually unlock most cards and with all the duplicates that you get you can disenchant them all and use that dust to craft the cards that you're missing.

Make sure you do all the quests available every day as they are the only decent way to get gold for purchasing cards quickly (aside from real money of course).

1. Complete all of the hidden Quest/Archivements in order to get gold/packs http://hearthstone.gamepedia.com/Quest#Unique_quests
2. Win 30 daily games (Every 3 wins you get 10 gold capped at 100 golds)
3. Save gold and buy all of the adventures (For every wing you will get minimum 1 legendary and most of them are very useful)
4. Try to get as high as posible in ladder (You will get some golden cards/dust)
5. Try to learn how to play arena propertly (If you do this you will get a lot of gold/packs/cards)
6. Pay real money (Obvious one)

As well as packs and crafting, you can earn legendary cards from adventures.

Adventures are made up of single-player encounters against AI bosses. Each is divided into wings, made up of 3-4 bosses. You earn cards for each boss you beat and a legendary card for beating all the bosses in a wing. Many of the legends from adventures are as good or better than legends from packs.

At 700g/wing, it is also cheaper than the 20 packs one would open on average to find a legendary card.

I would suggest you to play arena.

It needs some practice until you can draft properly, but for Example

http://www.heartharena.com/tierlist

helps to draft some good arena decks.

Each reward Contains a card pack and you have the possibility to get even more gold back. Additionaly some dust or cards are rewarded, too.