leeclose; Asking what mod to use in here is like tossing gasoiline on a campfire, repost city.
Here is a link to the SH3 MODS workshop
http://www.subsim.com/radioroom/forumdisplay.php?f=195
All of the supermods contain a vast amount of talent and each enhance the game. Some make radical changes to how the game works, such as bouyancy, renown, and identification. You can download each one and try them, but first I highly suggest you read each manual or read-me files, and read them again. Make sure the mod you choose makes the changes to the game you want or would like, and not what someone else wants for you.
I think everyone here would recomend JSGME. Once you get the hang of that nifty application installing / uninstalling mods is much easier.