Which ones better TK or WoC and why

I want to start an army and im not sure of which is a more solid army?

This is like comparing apples to oranges. The answer to this question is entirely subjective and only you can answer it based on your preference in playing style, aesthetics, and background of each army.

Start simple.. do you like the imagery of mummies, skeletons, and bone scorpions., or do you like the imagery of Grisly Warriors, barbarians, and nasty beasts of war. ?

In terms of game play, do you like a "in your face" I'm going to steamroll you with Close Combat type of army, or do you like a more subtle army with shooting, magic, and maneuvering as key components. ?

Lastly.. go to the store and look at the models. Do you like the workmanship of the more recently release WOC stuff, or do you still like the look of the older release Tomb King stuff?

If your asking about which is better in terms of competitive play, I would say that WOC are easier for a beginner to use, but can be equally vicious in the hands of a veteran gamer. Tomb Kings are more difficult for beginners , but once again, if played by a veteran can be very difficult to deal with .

So don't just consider which is more powerful... look at the other things that are important to you before you go spending any money.

Also, as, we've said before, you may want to wait until 8th edition to see how the rules will affect your army of choice.