I have a similar problem. I was a Marth main since I started playing, up until a couple of weeks ago when my playing partner switched mains to his secondary, so I switched to my own secondary, Peach, to level the playing field. I have more fun as Peach than Marth, but I still perform much better with him. My aforementioned playing partner-- the "Sheik main" (he's totally a Falcon main, he's just in denial)-- is the only person I have to play against on a regular basis, and he has the uncanny ability to somehow manage to get hit by every downsmash I throw out. This has fostered some bad habits in my Peach play, and that leads me to question whether I should go crawling back to Marth, stick with the uphill battle that is my Peach, or co-main them, which would be the obvious answer if I weren't so bad at the game. At this point, I think worrying about two characters is going to be too much, when I really should be worrying about simply getting better at the game. Any advice?