My opinion may not be totally fair, as I haven't tried both lately. But I used podpress for a while. THe problem was that every time WP did a major upgrade, podpress would quit working. I'm using podcastnig plugins for DJ music hosting on rvoodoo.com. Downtime sucks for my artists. So after about a year of having it break (once for many months) the powerpress plugin was offered.
I jumped ship, which was easy as powerpress offers an importer for podpress content. PowerPress is huge and powerful. Numerous media players, category casting, etc. I have never had downtime with powerpress. Also, they are very active in development. Any questions Ive had have been oanswered on their forums. They are very open to suggestion too.
So as a user who has relied on both for at least a year each, my vote is powerpress. I don't wanna knock podpress, I appreciate anyone making free plugins. And these big involved podcasting ones must take a fair bit of effort.
Just one note, neither plugin makes uploading a podcast easier. You upload it yourself. And link to it from within the plugin. I use ftp, as my files are usually over 200M. Browser uploads are unstable at that size. BUt I just ftp the file into my pocast directory I made, and link it when I make a post.