This is a solid response, so I'll just add to it.
The original Hek actually scales better because of the extra multishot mod. I'm also a huge fan of the Kohm, because it's just silly...but you have to put a fire rate mod on it to make it fun.
Technically, the phage is also a shotty, and it's pretty powerful.
I don't really have any non-prime assault rifles that I go back to, but I do get a lot of mileage out of the Tonkor, which is technically an assault rifle and is worth putting some work into IMO.
Sancti Tigris, Tigris Prime or Synoid Simulor are typically in my primary. Synoid Gammacor or Akstiletto Prime are usually in my secondary...occasionally Vaykor Marelok. I don't really care much about melee, but I usually default to Galatine Prime.
I think generally that the Syndicate weapons are the best options for 99.9% of the game, because they'll kill just as efficiently as top tier primes and also have the procs. They'll get slightly outpaced by some primes when enemies are at absurdly high levels.
The only non prime shotguns I've used and liked are Hek and Sobek. I've heard Hek scales very well into endgame with its augment. Sobek is good fun with its special mod, but it doesn't measure up to the ridiculous power of the better shotguns. I'd go back to the Hek regularly if I didn't opt to go the Vaykor Hek route.
The original Hek actually scales better because of the extra multishot mod. I'm also a huge fan of the Kohm, because it's just silly...but you have to put a fire rate mod on it to make it fun.
Technically, the phage is also a shotty, and it's pretty powerful.
For assault rifles, I like to use Dex Sybaris, which is a burst rifle that you can get for Warframe's anniversary coming up soon. It's burst fire though, not full auto. There are only two automatic "rifles" I use regularly. Quanta, which shoots continuous lasers and has a nice alt fire, is a weapon I used for a long time until I got Quanta Vandal. And then there's Ignis, which is a flamethrower.
I don't really have any non-prime assault rifles that I go back to, but I do get a lot of mileage out of the Tonkor, which is technically an assault rifle and is worth putting some work into IMO.
Sancti Tigris, Tigris Prime or Synoid Simulor are typically in my primary. Synoid Gammacor or Akstiletto Prime are usually in my secondary...occasionally Vaykor Marelok. I don't really care much about melee, but I usually default to Galatine Prime.
I think generally that the Syndicate weapons are the best options for 99.9% of the game, because they'll kill just as efficiently as top tier primes and also have the procs. They'll get slightly outpaced by some primes when enemies are at absurdly high levels.