I find it hilarious that some players in pub games think that picking viper or drow is a necessity for your team to win. I had a game last night where the guy on our team was saying "someone pick drow quick, someone pick drow, noooooo they got drow!" into the microphone, as if drow was a team killer.
I then proceeded to stomp the entire enemy team after randoming Slardar. Their drow melted like butter in every team fight, since I would pop speed, pop the armor-reducing ult on drow, run up and slam, then pound away (bashing in the proces) and watch her health drop in two seconds flat over and over. I went after drow first every team fight engagement and just trashed the hero, knowing that her ult is useless at close range, plus Slardar closes the gap so quickly with his speed and locks her down using bash & slam.
I'm going to start picking slardar now whenever I see the enemy team picking drow; it seems like he's the perfect anti-drow. By the end of the game I had 25-5 in terms of kills / deaths; I was getting reckless towards the end once I got my Heart of Tarrasque which is where the 5 deaths came from.