Stats. The more stars the better he is. To max in rank you need all versions. Apes can't change the dynamics of the getting the bots so no upgrading them to better stars No. But all bots trained help your level, squadcount and dupes can give you some nice stuff. Use spark on your 3* but not above lv5. Only use spark on lower when you're close to 3M spark and don't got energon.