Best is a relative term. I personally use GWX Gold for the vast, realistic overall gameplay enhancement it provides. I use MaGUI F w/TMT v2 (and some of its optional content) for the GUI and manual targeting. I also use a few select files from Thomsen's sound mod v3.2 to further enhance the immersion. And finally I use SH3 Commander 3.2 (w/GWX cfgs) for the wonderful career files it produces, and use the patrol log editor plug-in to flesh out my logbook
