I’ve been trying the different SMGs and this is my impression of them.
The main role of an SMG is as a CQB weapon. The demands of this are primarily large clip, high damage and full auto controllable. Which brings us to
CARB-9: it has all the CQB requirements which is what makes it so popular. It shines in no other areas. My favorite in cramped maps and as a secondary for medium body type, where my AR covers range work.
KROSS: it has low damage, but otherwise meets the CQB demands. It can counter this to some degree by its better accuracy, allowing you to open with headshots if your aim is good, and it does well at range. It doesn’t have the raw power of the CARB, but a competent player could do as well or better with the Kross except for very short range. I’m not good at headshots, so in my hands it feels underpowered.
Bulpdaun: with medium damage and good full auto control, and good accuracy, it is better for CQB than the Kross - until it runs out of ammo with its small clip (and no drum option). It has excellent ADS, making it a premium choice if range is needed from your SMG. My favorite choice for lights on open maps.
Galactic: Very large clip but low DPS. It has poor full auto control, but it builds recoil slowly and recovers from it very fast, allowing you to make repeated accurate long bursts. With good aim and burst discipline it feels like it should outshine the CARB at medium range, but it seems just a little too weak, only holding the advantage in the few cases where a drum CARB would hold too little ammo. I like it for holding well defended choke points and dislike it for everything else, generally making it too situational.
Tampa: good damage and clip size, but it is completely uncontrollable and the fast reload doesn’t seem to balance it in any way, rendering the weapon nearly useless outside of pointblank range.