Charizard with: Flamethrower, Fly, Dragon Claw, Earthquake.
Obviously Flamethrower is a powerful STAB move and THE move against Lorelai's Jynx. You need a Flyer so Charizard comes in handy here (not to mention that Fly is another powerful STAB move and sweeps all of Bruno's Fighting Types). Dragon Claw is a Powerful attack that compliments Charizard's high special attack (plus it could come in handy against Lance). Earthquake a the best coverage move you could teach it here- it gets rid of Charizard's 2 key weaknesses in Rock and Electric.
Lapras with: Surf, Ice Beam, Psychic, Thunderbolt
Lapras is easy to obtain as that guy from Silph Co. practically gives it to you and you're gonna need a Surfer (that's basically Lapras' gimmick). As I said, Surf is Lapras' gimmick as well as a powerful STAB move. It also handles Bruno's 2 Onix. Ice Beam is a no brainer- powerful STAB move, it take's care of Grass weakness, and it sweeps most of Lance's team. Psychic because it's a good, strong coverage move (especially against Agatha). Finally, Thunderbolt as it's another good, strong coverage move to have and comes in handy against Lance's Gyarados and Aerodactyl, and also against most of Lorelei's team. I recommend Thunderbolt over Thunder due to accuracy, however, Thunder is a more powerful attack and is easily obtainable at the Power Plant in case you don't want to spend more unnecessary time at the Game Corner (to get Thunderbolt). Also, try to get the Shell Armor ability- Lapras is bulky as it is and since Shell Armor prevents critical hits, you have a genuine wall here. Lapras' speed is an issue, however, the Quick Claw you get in the Safari Zone can help it's cause.
Snorlax with: Strength, Shadow Ball, Brick Break, Rest
Snorlax is an amazingly powerful Pokemon that's easy to obtain since you need to battle it to progress past Celadon City. You'll need Strength for Victory Road anyway and it's a powerful STAB move so why not? If you want to get rid of Strength after you exit Victory Road, however, you can replace it with either the Hyper Beam or Double Edge. These attacks are much stronger, however, I wouldn't recommend it (Hyper Beam's recharge and Double Edge recoil). Shadow Ball is a pain in the a** to obtain but that time in the game corner is worth it. Snorlax, as a Normal type, is immune to Ghost type attacks and and Shadow Ball is the best attack to take out Agatha's Ghosts. Brick Break is also a powerful coverage move to hake down Rock types, Steel Types, Ice Types, and other Normal Types. Rest is also very useful move to have in this game as the Poke Flute is a thing. It heals both status conditions and restores full HP whilst the Poke Flute can wake it only 1 turn after. Consider Snorlax's monstrous defences and HP and this is one of the toughest Pokemon to take down. Immunity and Thick Fat are both good abilities to have too. Immunity gives you, well, immunity from getting poisoned so that comes in handy against Agatha and Koga. Thick Fat raises resistance to Fire and Ice type attacks- great to have if you plan on using it against the likes of Blaine and Lorelei. Also, it's a good idea for you to catch enough Pokemon to at least get the Item Finder. It you go on the spots where the 2 Snorlax blocks you in the game and use the Item Finder, you get 2 Leftovers. For HP purposes, this is a good item to have on it.
