I always chose Hitmonlee back then, even though I loved both the Hitmons. I always hated the fact that I had to choose one, but I took advantage of that by playing Pokémon Stadium when using my game's save file with the Transfer Pak. Once you defeat the Elite Four in the Gym Leader Castle if my memory serves me correctly, you can be rewarded with the Hitmon that you didn't choose and even the other starters. I preferred Hitmonlee over Hitmonchan because I felt that he hit harder and had better moves. I wasn't a big fan of Hitmonchan's elemental punches back then because they were weak and, at least in generation I, the only real fighting move Hitmonchan could learn was Submission, which was good back then, but too weak for a recoil move, especially with Hitmonchan's Attack stat only being slightly above average. Pokémon like Machamp made better use of Submission with higher Attack and better bulk. Generation II did Hitmonchan a little bit more justice because I recall him being able to be bred better moves such as Hi Jump Kick, while still being able to learn those elemental punches. Nowadays, however, assuming that today's gameplay applies to older games or even a future potential gen I remake that isn't Pokémon Let's Go, I would probably choose Hitmonchan. Hitmonchan being able to hit harder with Iron Fist ability while holding an Expert Belt, physical damage for his elemental punches, and being able to recover HP with Drain Punch makes Hitmonchan fun to use these days regardless of what the Smogon competitive players might say about him. Hitmonlee is also fun to use thanks to his Reckless ability along with High Jump Kick, which can either do massive damage or result in massive damage. Either way, I love them both in different ways for different reasons.