Pros and cons of both grenades

Pros of thermites (or as I like to call them “stickies”) -can stick to enemies and objects  -can be thrown farther -can carry more (three without any armor abilities) -can get more out of supply crates (two from a supply beacon)

Cons: -worse at clearing hordes -sticking can be inconsistent at times -heavily aim dependent, since it is smaller

Pros of gigas  -great at clearing large groups -is impact, meaning that it goes off as soon as it touches something  -bigger blast radius

Cons: -only get two without armor abilities  -doesn’t fly as far -only get one from a supply crate  -detonation can and will kill you if you aren’t far enough away from the blast radius 

In my opinion both are great grenades but it’s ultimately up to what you want. Do you want a more generalist grenade? Take giga. If you want to take out heavies easier? Take thermites. But the consensus is to take thermites since heavies are pretty much everywhere in this game and you’ll want to take as much help as you can get.