I've been working with archives on MMH almost every day for over a 1 year now and here some advice I know.
If I were you I wouldn't pack a mod with 7zip especially when you don't know for sure if the mod doesn't have any missing .nif, .dds file, because 7zip doesn't support adding/deleting/renaming files in an existing archive. However even though WinRAR do support adding/deleting/renaming files in an existing archive (provided that the Read-Only attribute isn't attached to the file) it doesn't support adding/deleting/renaming an existing .7z archive.
There is another thing that's also important when packing a mod and that's about the directory structure and here is a good discussion even it's for Morrowind it also applies for Oblivion, Skyrim.
Okay 7zip do has its advantages compare to WinRAR and that's about the file size but that's about it. How you want to pack your mod is entirely up to you of course.
Sorry for a such long post, but I thought it would be best to explain.