Same old thing of just go with what feels best.
Otherwise... about the topic in question. I do think playing multiple characters can help advance your involvement with other characters as well. Playing Mk/Marth is vastly different from each other and still similar in many ways. While again being very different from Ganon when it comes to how to approach playing smash.
Using MK/Marth, you ave able to throw out some attacks without to much concern for safety due to disjoint. However, on a whiff Marth is punishable. On MK whiffing with certain moves is not actually super punishable by everyone. With ganon, he lacks any sort of edge through movement or disjoint, so he has to rely upon waiting for your opponent to run into your moves for the most part. Striving for ideal character play would help you understand more about some of the limiting and important things in smash and eventually help with whatever character you end up playing.
As for a good starter, there is no tier range that feels as a greater starter to just get into smash with. To be honest, I think the best starter would be any character that does not require you to need to do much decision making. For example, DDD is pretty much grab, ftilt, waddle dees, and Bair. You do not need much else on the ground until you score a hit on someone. Other characters are like Ike where again jab is his best move in pretty much 90% of situations on the ground. Etc. Other characters like that are Snake, Olimar, and MK I believe. You can play an effective play-style with these characters by doing only a few things. That I think can help teach the basics when you are not getting bogged down by all the possible choices you could make.