-Dratini - Low Tier
-Availability: In RB, you can theoretically get it as soon as you get to Celadon by buying it from the Game Corner. It is cheaper in Red but is at a lower level and therefore requires more grinding (level 18 for 2800 coins in Red and level 24 for 4600 coins in Blue). So either you’ll have to fork over a bit of money but spend time grinding, or you’ll get it at a more manageable level but have to spend up bigger. Neither is particularly desirable in an efficient playthrough. Alternatively, you can catch it in the Safari Zone with a Super Rod at level 15. This is probably a bit more practical and cheaper, but you are at the mercy of the Safari Zone mechanics and the level is a lot worse especially at that point in the game. In Yellow, it can only be obtained from the Safari Zone, and it is a bit rarer. It comes at the same level. Note that it is possible to catch Dragonair as well, but since you’ll likely have to go past level 30 for Dragonair to match your team, this isn’t really much of an advantage.
-Stats: Dragonite has the highest Attack in the game (134), great bulk (91/95/100) and decent Speed (80). Unfortunately this is nearly irrelevent because Dragonair evolves so late that Dragonite's stats are unavailable for most of the game. Instead, you are using Dragonair and its 84 Attack, 70 Speed and 61/65/70 bulk. It is fairly weak, and Dratini is even worse.
-Movepool: Dratini’s level up movepool is not that good. Hyper Beam comes way too late. Slam has decent power but is inaccurate, though Thunder Wave has some utility until stronger moves come along. Dratini can also use the Agility/Thunder Wave + Wrap combo to get around troublesome opponents, but this is slow and not very reliable. On the plus side, Dratini has great TM/HM compatibility. Pick from Surf, Ice Beam, Blizzard, Fire Blast, Thunderbolt or Body Slam. Obviously these comes with opportunity costs (except Surf) but chances are that you will have at least a few of these free so it isn’t so bad.
-Power: You are using Dragonair for most of the game and its low stats make it barely adequate. It does put work in and its wide TM compatibility ensure that it will be at least useful, but it will most likely be the weak link of the team.
-Type: It doesn’t learn any STAB moves sadly (not even Fly). From a defensive point of view, pure Dragon is nice. A strong set of resistances is backed up a general lack of Ice moves throughout the game. It is also unique to Dragonair. For types that Dragon doesn't resist, Dragonair will be using its stats and sadly these will sometimes fall short.
-Match-ups: Erika: Grass resistance, but you need Ice Beam to really be helpful at all. If you do then it should go ok though it won’t absolutely dominate the gym.
Koga: Neutral, in terms of type advantages. Koga sucks in RB so pretty much anything can work here (Dragonair is no exception but a full solo might be a bit much). Venonat is weak so Yellow is the same deal.
Sabrina: Alakazam will be too strong to handle. It doesn’t do well in the gym overall, though Thunderbolt can help against the Slowbro and Slowpoke used by the gym trainers.
Blaine: This gym is one of your best match-ups. Surf is probably the best move to teach Dragonair simply due to it being a HM rather than a TM, and Surf + Fire resistance gives it a good showing here. Don't underestimate the power of Arcanine's physical moves though.
Giovanni: Chances are you’ll have at least one move that hits Ground super-effective (Surf most likely), so you do alright here too.
Lorelei: Ice attacks are being thrown out a lot here so don’t bother.
Bruno: Onix dies to Surf. Dragonite should be strong enough to kill everything else, but Dragonair might struggle against Hitmonlee and Machamp.
Agatha: Golbat is weak to Thunderbolt and Ice Beam/Blizzard, but if it outspeeds and confuses you then you may lose anyway. Arbok shouldn’t be too much of an issue but Gengar can still win if you are unlucky.
Lance: Depends on your moves it has. Thunderbolt hits Gyarados, Ice Beam/Blizzard hits the dragons and Aerodactyl is weak to both. In Yellow you need to watch out for an ice attack from Lance’s Dragonair and Dragonite.
Blue: In theory, you can hit pretty much everything super-effectively but again it depends on what you gave it. Chances are that you'll be able to take on at least a few things though.
Additional comments: Dragonite is awesome, but because it evolves so late it may as well not exist before the Elite 4 (and even then you may not have it yet). Instead, what you are essentially getting is Dragonair, who has below average stats. Combine this with how tedious it can be to obtain in the first place and you have a pokemon that is clearly at home in Low tier.