This site will cover the best Starters for all regions with the physical-special split and their games, for which will give you the easiest time for an in-game playthrough for respective games. Obviously, there is no right or wrong choice, but there is one that will be the most helpful and beneficial for a playthrough for their respective regions. I will not look into the competitive field, though. To date, there are 8 pokemon regions, each will have a starter that will perform the best for that region. Things I will look at are stats, performance against gym leaders, evil teams and their leaders, Elite Four members, and champion.
Source: Eryizo (Link to his channel is right below)Eryizo Link