For me, I'd prefer a group of four as opposed to just a single companion. The three I'm thinking of would be the following:
Mallow: Excellent cook while being an excellent Group Leader(something I wish the Anime would give her the chance to shine but noooo... let's yield to Lillie or someone else. Sigh...). Plus her fondness for Grass Types is something I admire and will want in my group. Since her brother left on a journey, I feel she'd jump at the opportunity to do the same.
Dawn: No need to worry as she would say and that positive attitude would mesh well with Mallow. Her mixed typed arsenal and battling skills hopefully would rub off on Mallow. Conversely Dawn would benefit from Mallow's knowledge for Pokemon food. I wouldn't mind a Contest performer and a break from challenging Gyms certainly isn't a bad thing.
Serena: You might say she needs to be on her own to grow more as a character but I find she does best in a group. With Dawn as a friend and rival, the two of them can sharpen one another's skills. Serena also makes the most delectable treats one could ever have(I love people who can bake) that instantly earns her a spot on my group. Plus she can dance and I can't dance at all. Oh and having Sylveon is pure gravy.
With me being the only guy, it seems I'd be the odd man out but I really don't mind. Heck I might even prefer it over say a balanced group. Here's hoping the Anime looks at a Female heavy group in Generation 8. I'd add that if I had to pick one above, I'd probably go with Serena. Just would have to hit up Pokémon Centers or not be out on the road for long.