There are many ways to say it. I personally would say: 私は好きだよ。 watashi wa suki da yo. You can also say: 愛してる ai shiteru but I don't recommend it.

愛してる aisiteru But I think Japanese people often don't use it I usually use すきsuki or だいすきdaisuki You can say すき、すきだよ、すきです、だいすき、だいすきだよ、だいすきです You don't have to say object わたしは But if you want to say わたしは,it's Ok But I think people often say すきだよ than わたしはすきだよ Sorry my poor English