p i c h u
but in all seriousness play whoever you want. Maining a character is a personal choice in two ways:
1) You need to actually enjoy playing the character, so you have a reason to play the game, and
2) Your play style is not going to be suited to 'random online person #69's play-this-character'. You need to try out a lot of characters and determine who brings out the best in you.
I went through a similar character crisis in smash 4 and eventually settled on random because I wanted to play everyone, but that doesn't mean I don't play better with some characters and I don't enjoy some characters more than others. You're the same way.
If you want to be scientific about your decision, just try going into training and labbing out some characters that you are vaguely interested in, like Cloud. Try the different archetypes: try Ganon, try Lucina, try Pichu, try a Link (Toon Link! Toon Link! Toon Link!), try Cloud, try Sheik, try Olimar, try Daisy, try Snake, try Simon, try Fox, and then realize Pichu is really the only choice.
TLDR; play pichu