My suggestion would be go machine pistol and select the Remington Suppressor from Gun H(e)aven 3, page 9.
Accuracy 6; Damage 7P; AP -1; Mode SA/BF; RC -; Ammo 15(c); Availability: 6R; Cost „700
Standard Accessories/Modifications: Sound Suppressor
Suggested Accessories/Modifications: Personalized Grip („100), External Smartlink („200)
You boost the accuracy to 9 with this. Then take Automatics 6 (Machine Pistols +2), combined with an average agility of 3, and non-implant wireless smartlink bonus of 1 you have a dice pool of 12 to shoot things. This option offers a decent combination of damage potential and concealability over the assault rifle, while still allowing that option when subtlety is no longer needed. As always, consider your ammunition options as well. The real trick is how many non-magical skills do you want to devote points and Karma to? Automatics is versatile with MP, SMG, and AR offering three distinct responses through one skill; it's really kind of the "Swiss army" skill of the firearms group. Pistols offers limited range, and doesn't include MP, and Longarms lacks small, close range options (unless you consider the sawed-off T-250). For anyone not predominantly a shooty-type of character I think Automatics is probably the best choice. It has worked great for my Decker so far, though he sprung for an internal smartlink with improved rangefinder and uses an implanted Smartlink for +2 Dice Wireless.