In almost every game, my party is completely different from what I originally envisioned, and most of my early-game Pokemon don't make it with me to the end of the game. My biggest notable exception to this was Butterfree in HeartGold. It was the first Pokemon that I caught, and it stayed in my party (generally as my lead Pokemon so I could have it follow me around) through all 16 Gym Badges, multiple victories over the Elite Four, and even in my battle against Red.