Honestly? I normally go with a light or heavy pistol and then a melee weapon for my mages. Sometimes archery, if it fits the character better. While a mage with an assault rifle works fine, I typically don't see the need for it. If you're looking for a way to keep people's heads down while you cast, there are better ways than big weapons that most corpsec will notice (concealing an assault rifle isn't exactly easy). Two keys: spell selection and smoke grenades. With the proper spells, you ARE the weapon. With smoke grenades and astral perception, you can see the targets, but they can't see you. Let me put it this way. When corpsec looks for targets, they start with the mage and the people with the heaviest weapons. You're starting to look like both. And pistols are easier to get through security, more likely to be legal in a jurisdiction, and don't draw nearly the attention larger weapons do. Also, they're much more common, since there are a few million Predator Vs out there, and they're cheap, meaning you can wipe 'em and toss 'em if you need to.
IMO, spray and pray is crap, and a waste of ammo. Suppressive fire, on the other hand, is a great tactic, that works best for a Face, Drone, or secondary gunman, not someone who has other options to bring to the table, like a mage. The Mass Agony spell alone is enough to ruin a whole crew's day. Fireball is the quintessential mage's "Go Away" card. Improved Invisibility means you can slip around enemies, and put two to the side of their head. Even without magic, there's a reason why soldiers use controlled bursts rather than spray and pray. You won't hit a damn thing.
So my recommendations for skill/gun for a mage would be: Pistols (Specialization in either Tasers or Semi-automatics) with either a taser of choice or Predator V (clips of APDS and SnS to switch as needed), Unarmed combat (Knucks or shock hand), or Blades (Katana). Again, this follows the line of reasoning that when you are a walking restricted weapon (being a mage) and can summon fire support (spirits) it is best to consider what personal weapons are easy to get through checkpoints with minimal police interest. And automatic weapons and shotguns draw far more interest than a sprawl dweller with one of the most ubiquitous handguns on the market. Same as when you're driving with a load of novacoke in your car. The fewer reasons you give the cops to take interest in your vehicle, the better.