Which Mod should i use?

This is most certainly the right place to ask such question!
As Steve described, choosing which megamod to use (if any) should base on your personal preference on what do you want from the game. More detailed descriptions and comparisons can be found on forums, for example:
http://www.subsim.com/radioroom/show...13#post2192013 (might not reflect everyone's opinion)

What megamods to add on top of those is also a matter of preference. You can find modlists posted by salty veterans from which you can draw inspiration. Popular enhancements are esthetic mods like widegui, MEP, soundpacks etc. Some of these are also included in some megamods like LSH. Then there are lots of little things like removing the "jawohl herr kaleun" after a command which might make your experience a bit better.

Welcome aboard kaleun!

PS. I think custom avatar requires a donation to Subsim