I saw a thread on heroesnexus.com that had some misinformation on it about "junglers" so i wrote a reply and i wanted to post it here to maybe end some confusion.
Sending anything other than a specialist to do mercs is a waste, Gazlow is the best then Witch doctor I also saw someone say mercs weren't worth it and that's just misinformation, Mercs are a huge part of the game. Gazlow can get Giants at level one and knights at four and boss at 10. Wtich Doctor can get Giants at level one it just takes longer but, it is a waste of time for Witch Doctor to go for knights before 10 but, once you have your Ult you crush them and at 16 Witch Doctor can solo the Boss merc easily. That being said, If you don't have a specialist, A tank and Assassin are your best bet for mercs, A tank could solo them but it would take way to long, so send an assassin along with the tank to melt the mercs and you're good to go.
On the topic of lane experience it is needed yes but, you have to learn very fast when to leave your lane and your exp for team fights and objectives. I cant tell you how many games I've lost cause one person thought they were THE hero of the storm farming their lane and not helping team fights Or Objectives but, If you are farming Lane EXP instead of going for coins on Blackheart's bay you're bad and you should feel bad, Assassins and Supports are the worst about doing this it seems, Lookin at you Raynor and Malfurion.
If your team has a Nova or Zeratul, adjustments should be made to let them roam and gank lanes to keep the enemy on their toes, But Nova/Zeratul also need to make sure they are ready to haul ass to objectives, Coins, Tributes, or shrines, Skulls/Mercs depending on which golem it is....Never go skulls on the first golem!