I feel that I should point out that Heimy doesn't have an afro. An experiment caused his brain to grow so big that it ruptured his skull and is now only kept inside his head by heavily steached out skin.
Heimer is capable of handling his own against those two most of the time really. Bots are just plain stupid, and most players are too cowardly to go for a direct attack (since Heimer can dish out ridiculous amounts of fast damage on the first jerk to try and attack him). A full health Cho goes down like the titanic if heimer would unload on him.
Now if it were Fiddlesticks and one of those two, different story. His fear attack is a force to be reckoned with, and since heimer does rely on some positioning for his turrets, and "fast" attacking, fearing him is usually a very effective way to take him out.
That said, I love the heimerdinger character. I'm a terrible pvp player, but since he's so easy to handle, I can actually enjoy most pvp matches ^__^.
Ehh, Nunu would instantly eat all his turrets, meaning he'd have to rely on only his grenades and rockets for damage, and since both Nunu and Cho'gath are tanky and capable of healing, I'm pretty sure his tower would be down quickly.
Unless, of course, that Fiddlesticks pulls off some amazing ganks.
Nunu would be able to take down both turrets with his ultimate, true. But his ultimate takes time to execute and is incredibly easy to avoid. That said, it takes a few seconds and before he is able to take down the turrets, they can (depending on their target) deplete his health by quite a bit. Heimer can also throw in his grenade for a stun, effectively ruin the ultimate attempt entirely.
And Cho isnt as effective as a tank as you might think. He has a lot of health, but I found him to be surprisingly squishy if he doesnt have any good armor or magic resistance.
Now, I'm not saying Heimer would always win against those two. Against 2 competent players he would lose after a while. Problem is, most players simply arent competent and shit bricks whenever they encounter his two turrets.
there's still 2 of them, and they will still do some damage. Add that Heimers 3rd attack (the grenade) has a stun/slowdown on it, and that his ultimate fully heals and improves the speed OF the turrets..
Don't underestimate heimer. While he by no means has offensive capabilities that far surpass true pushers/tanks, he can still deal out a respectable amount of damages.