Ubuntu, used to use VIM exclusively, now I'm trying a variety of IDEs at the moment (found out I prefer something that can remember the state of the project, to just VIM + NerdTree).
My experience so far:
* Geany (programmer's editor using GTK+) is simple and fast; if I'm using a graphical IDE, I'd like code completion (that can complete the code I wrote, not just stdlib) though
* Komodo (Edit) 6.0 (built on top of XUL) is fairly comprehensive; I keep getting bugs (or weird behaviour) with it (last time it wouldn't remember the custom python path for code completion), and feels a bit sluggish
* So far I like Wing IDE (commercial, I'm having a trial run atm). Comprehensive (if you go with the pro variant which costs a bit more, but hey, if I'm spending a lot of hours every day in it, it's worth it) & feels fast to me.
I haven't tried Aptana or PyDev. I have this (irrational?) feeling about Eclipse being huge, slow, and memory hog. I've used it a couple years ago (for some Java coding) and never felt good using it; and it was the bloatest application on my system (yes, even more than OpenOffice). From the comments here (so far), it looks its more or less the same nowadays...