私わKatherineです Or 私の名前は...?
Well the title says it all; which one is used to be used or can I use both?
Please let me know.

Question

私わKatherineです Or  私の名前は...?
Well the title says it all; which one is used to be used or can I use both? 
Please let me know.

Answer

私はKatherine(キャサリン)と言います。or 私の名前はKatherine(キャサリン）です。
In my humble opinion, 「私はKatherine (キャサリン) です。」is okay, but to be more specific, those two sentences would be recommended.

Answer

the topic particle is は. You got it right in the second example. But the first would have to be written as
私はKatherineです.