Formal:
* Vous l'aimez beaucoup. (You love it a lot.) This is the most formal way to say it.
* Vous l'adorez. (You adore it.) This is also a formal way to say it, but implies a higher level of love.
Informal:
* Tu l'aimes beaucoup. (You love it a lot.) This is the informal way to say it, used with friends and family.
* Tu l'adores. (You adore it.) This is also an informal way to say it, but implies a higher level of love.
* T'aimes ça ? (Do you like this?) This is a casual way to ask if someone likes something.
The best way to choose the right phrase is to consider the situation and your relationship with the person you are speaking to.