Depends on what kind of game mod do you like.. I would like to suggest this list of SINS mods but which one to choose are up to you..
Maelstrom Mod (Enhancement-type Mod)
Star Wars Interregnum Mod + E4X Mod (Enhancement-type + Expansion-type Mod)
Crazy Mod (Enhancement-type Mod)
Star Trek Armada 3 Nemesis (Total Conversion Mod)
Stargate Races (Expansion-type Mod)
There's a few others mod but these mods mentioned above are my favorite choice of mod for the time being...
Depends on your favorite type of game like Star Wars, Stargate, Star Trek or related stuff.. IT'S UP TO YOU...
But 1st of all, you need Sins Rebellion v1.90 version but for Crazy Mod, you need to use SINS Rebellion v1.86 version as they're currently working on it's next update that works on v1.90 but unknown when it'll be released..
FYI: I don't know much about Total Conversion-type Mod much, i'm sorry in advance...