And Naix I think Mekkah already used Farfethd in a play (I could be wrong though, but I think he told me once he used it), so you should probably do Spearow.
Mekkah used it, but my write up is still there, and honestly it's pretty crap.
Farfetch'd - Low Tier (Top Tier as HM Slave; Bottom tier as a battler)
Availability: Somewhat early, as you trade Spearow for it in Vermilion city. Notably, you get it in the same town as Cut.
Stats: Crap, don't bother battling with this... just don't... Pidgey is better. Doduo is better. Spearow is probably your best in-game Normal-/Flying-type (and it's not that great at all).
Movepool: Cut + Fly... NICE!! Yeah, Farfetch'd's biggest selling point is being the only Pokemon to learn Cut + Fly (except for Charizard). In fact it's the only Pokemon in the game to learn Fly + any other HM, except for Charizard (don't teach Charizard cut... also you're Charmeleon won't evolve until long after you've gotten Fly) and Fly + Flash Zapdos (which is pointless since you're not going to waste Zapdos that way, and you've gotten through Rock Tunnel by the time you get Zados). Cut + Fly is a pretty useful HM combination around the time you get Fly, letting you chop your way into Celadon City Gym, and around the Safari Zone and surrounding routes while also boasting the ability to move freely between Celadon, Lavender, Saffron and Fushia. Farfetch'd is undoubtedly one of the best HM slaves in the game.
Power: Quack
Type: It gets STAB on Cut and Fly... Quack
Match-ups:
All: Quack
Additional Comments: Considering you're just going to catch a Spearow for it (which are really easy to find east of Vermilion, and not too hard to find before Mt. Moon), and how much time Farfetch'd's Fly + Cut combo will save you mid-game, it's probably worth taking the time to trade for in Vermilion. Just don't battle with it... EVER; though like all HM slaves, it makes a good sacrifice when you need to make a safe switch-in. However, if you want a fly slave you won't feel embarrassed riding on... go with Pidgeot, Charizard, or Articuno...
I think this would be better:
Farfetch'd (RB) - Mid Tier (overall) Fighting: low / Utility: top
Availability: Somewhat early, as you trade Spearow for it in Vermilion city. BTW, you can catch Spearow easily just outside Vermilion if you haven't got one already.
Stats: Its stats are terrible. It is outclassed by every other normal/flying type in the game in stats, even Pidgeot is better.
Movepool: Cut + Fly... NICE!! Farfetch'd is the only Pokemon in the game to get Cut + Fly, two relatively poorly distributed HM moves. Dux is obtained in the same town as Cut, so the same time you'll start needing him. He's also there ready and waiting when you get Fly. Cut + Fly is incredibly useful in moving in and around Celadon and Fusia, and moving between all the main mid-game towns. This makes Farfetch'd arguably the most useful HM slave in the whole game. Also, Farfetch'd gets the 140 base power Slash (with the crit), and Swords Dance (which works with Fly or Hyper Beam). DUX also gets boosted experience points. Not saying that any of this makes it better than a Dodrio or Fearow, but it's not completely unusable as a battler.
Power: Quack Slash / Swords Dance kind of make up for crappy ATK.
Type: A million other options with this typing, which is just ok. Repetitive STABs, not-so-useful resistances.
Match-ups:
Lt. Surge: No.
Erika: You get Fly in Celadon, so Farfetch'd can basically roll through her, just like any flying type in Celadon.
Koga: You're too weak to do much here as his pokes have great DEF... too bad there are no venonats...
Sabrina: You will probably get fried before you get to do much. If for some reason you don't get killed instantly, Slash will hit her pokes very hard.
Blaine: Farfetch'd can beat growlithe, and can do a bit of damage. Don't expect it to sweep the gym though...
Giovanni: His pokes mostly have great DEF and hit hard. Rhydon laughs at anything and everything you could do. This is not a great gym for DUX.
Lorelei: Beam'd to death...
Bruno: If you have leveled up sufficiently, Dux can kind of help against the fighting types.
Agatha: Since her pokes are often faster, expect to be confused and haxed a lot. You can do some damage with SD + Fly if you manage to attack alright.
Lance: Hyper Beam'd to death...
Rival: Pokemon you can beat: Exeggcutor. Pidgeot too. Time your Fly to dodge Sky Attack and you'll be fine. With SD up it can potentially be helpful against things not named Rhydon.
Additional Comments: There are 2 things a player should do to make his RB run faster and more convenient/fun. The first is get the bicycle, the second is add DUX to his party. Just remember that DUX is probably the best HM slave in all the RBY universe. If we were tiering it purely based on utility, it would be top tier. Unless you really hate the mental image of dry humping a small duck to go from town to town, there's really no reason why you WOULDN'T have DUX on your team between Vermillion/Lavender/Saffron/Fushia. It's just so good as a HM slave, unless you enjoy inconvenience, DUX should probably be on your RB team at some point.