nik4nix
Nik plugins on Ubuntu standalone or with Picasa3
..., because there are some UI glitches related to gtk widgetset if you compile for Linux - the UI looks better in native Windows version (this can be fixed in the future).
Even if you use native Windows version on Linux via wine, the app will be aware of wine and will still be integrated with your Ubuntu desktop and will be integrated with supported apps on it, like Gimp, Pinta, Darktable, Nautilus, etc. It will still talk to your shell, and provide all the integration with your Linux.