Honestly as a newcomer experiment with all characters and see which ones feel more natural. For example, I opted to go sheik because of her easy combos and overall mobility, which was much closer to what I experienced in other smash titles, sorta
. But yeah, Captain Falcon and Marth are superb choices, as well as Falco, because as you learn how to play the three, you easily learn fundamentals such as spacing, L canceling, etc., which you can then transfer to virtually every other character. However, do not let this deter you from changing your mind, feel free to change your mind. If you don't like the characters and you feel the need to find a new main, by all means do it. Experiment with all the high tiers (Fox, Falco, Puff, Sheik, ...) until you find one that suits your playstyle. We can't force you to play Fox, and neither can yourself. You have a large, unique roster to choose from.