|P is for Practical|
You don't say WHY PM is your least favorite?
There are several reasons. I won't describe them all, some are just vague, and not worth discussing.
One major con against perlmonks is its user interface. It's web based, which is just horrible compared to usenet, mailinglist, IRC or MUDs, all of which I can do from an xterm. For usenet and mailinglist, where you write articles, just like with perlmonks, you can do the editing in your favourite editor *IN PLAIN TEXT*. With perlmonks, you have to use a small textarea, writing in some poorly defined HTML derived markup. You don't even have the option to write in plain text, or POD. It's a lot easier to type C<$_> than it is to do <code>$_</code> (specially considering that HTML already has a CODE element). Mailinglist and usenet articles I can automatically file - not so with Perlmonks.
Perlmonks is the only community I frequently visit that has thrown adds at me. I very seldomly see spam in the usenet groups I visit, or on the mailinglists - they have been filtered out before reaching me.
Also, I find it much harder to 'notice' individuals on Perlmonks. On other forums, I find it easier to notice others - people spring out because of their particular knowledge, style, behaviour, signature, (dis-)likes, etc. There are a few names here I pay attention too, but that's usually because I know the names from other elsewhere.
Note that I'm not saying I don't like Perlmonks, I wouldn't be here if that was true. But if I have to rank the communities I visit, Perlmonks would end last.