Formal:
* Eu também a amo. (I also love you.) - This is a very formal way to say it and is typically used when addressing someone you don't know very well or when you want to be respectful.
* Eu também o amo. (I also love you.) - This is the masculine form of the previous sentence.
Informal:
* Eu também te amo. (I love you too.) - This is the most common and natural way to say it in informal contexts.
* Eu também amo você. (I also love you.) - This is another informal way to say it, but it's slightly less common than the previous option.
* Eu te amo também. (I love you too.) - This is a more affectionate way to say it.
* Amo você também. (I love you too.) - This is another affectionate way to say it, but it's less common than the previous option.
More affectionate:
* Amo-te também. (I love you too.) - This is a very affectionate way to say it, often used between lovers or close friends.
The best option will depend on your relationship with the person you are talking to and the tone you want to convey.