I've been running ProCamera 8 for some time and I like it, but I think it depends on the desktop app combo that you're running.
ProCamera 8 can change the aspect ratio, ISO value, white balance, and shutter speed within the app as you're shooting. But if you're running a Mac, then all of those (except shutter speed) can be adjusted within iPhoto which is free. If you're using a PC you may end up with PhotoShop Elements for $150+ to accomplish these tasks.
No matter the app, IMO the issue is ease of use. I use a cell phone camera most when the kids are playing, the dog is doing something funny, or I'm snapping a photo on a ski run. For these cases it's nice to have the quick access button from the lock screen of the Apple Camera. Unfortunately this shortcut cannot be replaced with the app of your choice.