Is not that PHP will teach you bad habits, the thing is that PHP used to be a non object oriented, then on version 5, a very good support for the object oriented was added, yet most the core functionality is still grouped in functions. This is about to change with PHP6 which is entirely object oriented.
Does this mean PHP will teach you bad habits? no unless you don't really want to learn how to program and just memorize lines, which doesn't seem to be the case.
Speaking of python, it's a great language, specially since Py3k is out, you should learn python, even if you don't use it for the web(and if you do, check out Django).
As of .Net, yes, it's all pretty and simple, and even I like C#'s syntax, but it only runs on windows, and without flaming windows, there is a reason 99% of the servers on this planet use some form of unix, being linux and freebsd among the most common.
Btw, you might also wanna take a look at Ruby(and it's lovely Ruby On Rails), personally, ruby is not "my" language, but it's certainly a very interesting choice.