I haven't bothered with Pashua, but PyObjC is fairly easy to get started with and works quite well. The only caveat is that the apps you write using the bridge only run on the same major OS version. i.e. apps writter on 10.3.x will only run on 10.3.x and not 10.2.x. Aside from this, for a lot of quick projects, it makes writting a full cocoa app real fast and easy. An example would be the freeware pyWeather that is available on my site. It was coded in just and hour or two using the PyObjC bridge.

PyObjC is an entirely different class than something like Pashua. The former is an entire bridge. The latter appears to be a way to put up Aqua dialogs.

You can do this with PyObjC as well, and by using the ObjC methods via Python, off the top of my head, without actually writing a quickie app, you would import objc, appkit, foudation. Then just use the exposed classes. dlg = NSAlert_alloc_init_()
and apply the options you want, then call dlg.runmodal_()

I have used this in several PyObjC apps, as well as in some of my personal scripts that are command line python scripts or applets.