Originally Posted by Lameador
Both do 80 dmg, but infinity's edge passive is awesome. Especially on Ashe or other chars with crit boosts.
Black Cleaver is 80 dmg and a good armor debuff passive
Infinity Edge is 80 dmg, at least as good passive AND 20% critical.
The 20% crit is definitely worth the 1000 extra gold, especially as it comboes with the passive.
BTW, why choosing ? Get both.
Getting both is usually not an option in a higher end game. I used to get all the items I wanted every game, then my ELO got high enough that I usually run into good opposition and the games don't go beyond 45 minutes very often.
Black Cleaver is the better option on the majority of DPS heroes, IMO. Take it on Ashe over the Infinity Edge next time, you'll be surprised at the DPS boost. The armor you negate on the enemy hero helps a ton.
The biggest thing is that it's available at about 1000 gold cheaper, and is a significant boost in your damage output, meaning you can kill heroes and towers that much easier.