"I like cameras."
I think (I'm not sure) that from more to less formal it would be "好きです", then "好きだ", then just "好き". I've heard "confessions" in anime where the entire sentance was just "好き", when the characters are already close friends. I'm not sure at what "level" of closeness you'd need to be to use each form though.
は marks the topic of conversation while が marks the subject of a sentence. So it could be like "lets have a conversation about cameras; do you like cameras?" (は) versus something like "lets have a conversation about hobbies; I personally like cameras specifically" (wherein "hobbies" could be marked with は as it is the topic of conversation, and "cameras" with が as it is the subject of the sentence following the topic marker). Its a subtle difference but it kind of gets easier with practice