This seems to be the ultimate 'get away from me' weapon. Rocket Launcher OR Grenade Launcher with a Safety Guard. The Bouncing Bolas were surprisingly more effective than the other versions of the bolas. Line Gun was decent, but I prefer the Plasma Cutter over it. The Carbine was actually my second favorite, very powerful, high ROF, and very large mag for a semi-auto rifle. The Bullpup was the best, but none of the Military Engine weapons really disappointed me. Very high damage per shot for an auto weapon and super accurate. Mag size is decent, but still much smaller than the Chain Gun. This is the fastest killer I found among the automatic weapons. Might be worth it to use CLIP chips instead of ROF chips since it has very low mag size. Super powerful, super fast projectile, and a very high ROF (that could go even higher because I only have 3DAM+2ROF chips), and an almost instant reload. I also NEVER mix and match upper and lower tools since they share an ammo magazine, I always just put the same tool on the bottom. I don't have all the best stuff, but I have eight 3DAM+3CLIP chips and eight 3DAM+2ROF chips, so I got an idea of almost every weapons' full potential. I did a bunch of testing on Impossible just last night. The Chain Gun does have some competition though. Apparently Chain Gun + Force Gun was a popular combo, but I didn't like the Force Gun when I tested it. And I've seen a lot of other people saying the same thing.

Playing by myself, I arrived at the same conclusion you did - that Chain Gun is the best. My below opinion is still mostly correct, though I might put shotgun or plasma cutter alongside chaingun as the chaingun isnt hitscan, is somewhat redundant because of the Flame Glaze Force Gun, and clip size isn't as important in this game as ROF. You want to have different weapon types on a single frame, they do NOT share the same magazine as I say later. The order in which you unlock parts in a fresh playthrough matters, as the Ripper starts out great before becoming garbage rapidly.

First of all, the Force Gun with Flame Glaze will kill almost everything for you. EDIT: Editing my two year old comment to say that parts of my opinion are garbage.

Best custom dead space 3 weapons