I use Ubuntu, so I don't know if these are in Debian as well, but Jockey and Ubuntu Software Center come to mind.
My main issue with them is the common symptom where both "hang" or "freeze" for a few seconds. Visually this can look like the window gets grayed out for a bit (common in Jockey) or it it is just stuck for a few seconds with no clear indication anything is happening (more common in Software Center).
EDIT: I should note that I've previously written a few PyGTK apps and have recently started writing Ubuntu Touch apps via their Ubuntu SDK (Qt/QML). I've found that Qt/QML/Ubuntu SDK is a much better experience in both writing the app and the responsiveness of the resulting application. And I'm by no means proficient in QML, I'm just starting out.
My main issue with them is the common symptom where both "hang" or "freeze" for a few seconds. Visually this can look like the window gets grayed out for a bit (common in Jockey) or it it is just stuck for a few seconds with no clear indication anything is happening (more common in Software Center).
EDIT: I should note that I've previously written a few PyGTK apps and have recently started writing Ubuntu Touch apps via their Ubuntu SDK (Qt/QML). I've found that Qt/QML/Ubuntu SDK is a much better experience in both writing the app and the responsiveness of the resulting application. And I'm by no means proficient in QML, I'm just starting out.