Joyeux Noël - Joyful Christmas

It is the most common way to wish someone merry christmas

Tous mes meilleurs vœux de Noël - All My Best Wished For Christmas

If you are in a professional environment, it is the best way to greet people with warm wishes of X-mas

Je vous souhaite un joyeux Noël - I wish You A Merry Christmas

If you want to be formal, you can use this greeting to greet one or several people

Je te souhaite un joyeux Noël - I Wish You A Merry Christmas

You can use this phrase when you are talking to one person and are being informal

Joyeuses fêtes - Happy Holidays

You can use Joyeuses fêtes or Joyeuses fêtes de fin d’année when you want to wish happy holidays

Meilleurs voeux pour la nouvelle année - Greetings For New Year

You can use this phrase if you want to wish new year's wishes but in a formal way

Meilleurs voeux pour les fêtes - Greetings For The Holidays

If you wish to be informal in your new holidays greetings, use Meilleurs voeux or Meilleurs voeux pour les fêtes

Bonnes fêtes (de fin d’année) - Happy Holidays

It is another popular phrase used in French to greet people with happy holiday wishes