There are people who start adding salt to their food before they even taste it. If you are one of those people, (or a person like me) you can answer this question before you've even seen FO4. In my case my answer is obvious based on all the other FO games I have played, and my play style:
I need a mod that will increase my carry weight (way more than a perk) because I am such a packrat. I need to carry everything. If I clear out a den of raiders, as far as I am concerned, everything in that building belongs to me!
I justify the "cheat" in my head as non-unbalancing, but simply as saving my time. My character could have walked back and forth 20 times to carry all that crap to the store, but with the "weight mod" I only need to sit through one of those trips.
How about you? What are your must-have mods?