If you plan on parking the domain the .info, .net and .org will be less valuable because far fewer people will use direct navigation to get to it.
I agree with nrmillions about whether to register the other extensions, it all depends on whether you plan to develop the .com as a brand or sell it on to somebody who might want to develop it as a brand.
If I buy a generic word or phrase with an obvious use that can't be trademarked, I ignore the other extensions if they are already registered. If I paid $x,xxx+ l would register other extensions if they were still available but chances are they won't be.
If I buy a very brandable .com on the aftermarket I would go after the other extensions and slightly overpay if needs be to protect my .com. I figure if I sell the .com having the other extensions will add value, if I develop it, it will cut down on legal disputes.
I am more likely to buy a very brandable .com if I think I can hoover up the other extensions. If a .com is for sale at a fixed price, I will make very low offers for the .info, .net and .org first, to see if I can open up the owners before buying the .com
When I first got into domains I would often register every extension available if I found a .com I liked but I usually lived to regret it and let everything go apart from the .com the following year to keep my options open and my reregistration costs down. How many very successful branded sites do you know that aren't .com? It's only going to be a threat if the keyword or phrase is an unusually good fit with another extension, which is sometimes the case with .info and less frequently with .org.
Realistically, if a .com is unregistered it's not as good as you think it is, so there is probably no point clearing the other extensions completely off the shelf. It makes more sense to register just the .com and register everything else if you ever develop it. If the other extensions do go in the meantime, you can always protect yourself with a trademark.
