Isn't the Cat mod SMG only? if so, the choice is obvious.
Actually, go SMG anyway, since ARs suck.
I've only gotten two good SMGs my entire playthrough to 50 on my siren, and those were Good Touch and Bad Touch. I've gotten much better ARs. --- I could see you, but I couldn't hear you You were holding your hat in the breeze Turning away from me In this moment you were stolen...
Easily obtainable SMGs stronger than most legendary ARs:
Plasma Casters. If you're willing to play a little dirty, you can use the read-only profile trick to farm the Sanctuary chest for plasma casters. Maliwan Plasma Casters deal nearly double the listed damage on its item card due to a minor explosive effect, while Hyperion Plasma Casters have superior damage, rate of fire and accuracy. Obtaining one with a projectile speed boosting prefix covers up their main disadvantage of low muzzle velocity.
Chulainn, being the only dual element weapon in the game and having the fantastic element combination of Slag and Shock (and a ridiculously high elemental effect chance of 46% slag and 36% electrocute), is an extremely good SMG. The only drawback is it slags you as well, so you need to play a lot more cautiously, but if you work around it with a turtle shield, it can serve you very well.
Sandhawk is one of the highest damaging guns (bar evil smasher glitched weapons) when paired with a Bee. Muzzle velocity is really low though, so you'll be using it more against raid bosses who move predictably than in extended mob firefights.
I got an E-Tech AR at 28 that lasted me till 40...it was basically an SMG with AR damage. Had probably a 4x scope, 45 round mag, 2.0 reload time, 93% accuracy, 0 recoil, very high bullet speed, and it did fire damage. I was going through shielded enemies in about 2 seconds, unshielded stuff died even faster.
A level 50 version of that would probably be as good as any SMG.
anyway the point is loot is random..use whatever you have that works best. --- I could see you, but I couldn't hear you You were holding your hat in the breeze Turning away from me In this moment you were stolen...
The point is, good SMGs are much more common than good ARs. Yes, a good AR is out there, a good elemental SMG is found every play session it seems. --- “History shows again and again / How nature points up the folly of men.” Official Aquaman C&GN
Yes the SMGs are generally easier to find. The Lascaux is a pretty damn good weapon, and that's an automatic find. And substandard Rifles are awful. When you get a good Rifle it's a godsend though.
I generally use both Rifles and SMGs (and that's for all my characters). But with Maya I'd only tend to use Cat mods against bosses. For all else I find it best to take something that benefits all your weapons.