>>47724044To avoid gaining too much XP for my starter while also not having to look up the levels of gym leaders and the like, I rotate my starter with a second Pokemon. So, my starter gains a level, I swap to the second Pokemon, swap from that Pokemon to my starter when it gains a level, repeat. It essentially halves the amount of XP you would otherwise gain in a traditional "use your starter for everything" run. The other four slots are HM slaves and the like
That being said, my second Pokemon is almost always the "route 1 rodent" of that gen. There are a couple of gens in which I will use the "route 1 bird" instead, but the rodents are almost-always a constant companion all the way to the Champion battle. Linoone is still the best I've used so far, but Bibarel was also really good.