ok lets compare the two


scyther  basic pokemon 70 hp 
attacks 
swords dance (for one green energy) during ur next turn slash base damage is 
60 
slash (for three colorless)  30 damage 
weakness to fire restance to fighting retreate cost zero


farfetch'd basic pokemon 50 hp 
attacks 
leek slap (for one colorless ) flip coin if heads does 30 damage if not does 
nothing either way u cant use it again unless u scoop him or revieve him 
pot smash (for three colorless) 
weakness electric restance fighting  retreat cost one colorless


now lets compare 
farfetch'd 50 hp ok  
scyther 70 better 
attacks leek slap can come in handy if ur lucky 
swords dance is useless is scyther is fully powered 
both basic 
both fighting resistance 
farfetch'd retreat 1 good 
scyther retreat ZERO great 
farfetch'd weakness electric not good against haymakers  wich have buzz
scyther weakness fire  not good against haymaker wit magmar 


what  the main reason that brings poor scyther down is his weakness to fire 
which is a majorly used type but he makes up for it in his retreat cost  his 
swords dance is only useful if u have a grass on him and then get a double 
colorless 
otherwise crap farfetch'd leek slap is too unreliable to really count on in a 
jam but its cost is appealing to people the thing that brings farfetch'd down 
is his hp and retreat but his retreat aint that bad both are vulnerable to 
super energy removal more scyther than  farfetch'd only if u havent used leek 
slap yet though  its really a toss up between the two i personaly like them 
both