I'mma jump in here and tell you to get a Combee. You can catch them by headbutting trees outside the grand hall. If it has hustle it can be surprisingly useful, and Vespiquen is possibly the best non-starter pokemon available for the early game. If that's not your thing then I can personally recommend technician Meowth, Teddiursa, Budew, Hoothoot, and surprisingly Grimer as excellent pokemon available before the first gym.