If EVERYONE is playing a pregen, you can do it OK by yanking the ultra shitty people.
The Combat Mage, Drone Rigger, Enforcer, Face (in fairness, only by dint of being the only face), Gunslinger Adept, Hacker, Occult Investigator, Radical Eco-Shaman, Street Samurai, Street Shaman, and Technomancer are all functional characters, in the sense that they have a job and can do it.
The Covert Ops Specialist and Weapons Specialist both have jobs, but suck at them. The Sprawl Ganger I don't know WTF he was supposed to be good at, but he isn't good at anything except sucking and being useless. The Smuggler can't smuggle shit, but is an acceptable getaway driver; however, I don't know how many players want to play 'wait in the van while everyone else goes shadowrunning.' (the drone rigger, by contrast, can send drones along). The Bounty Hunter is not very good at hunting people and even worse at winning fights when he finds them; it's particularly bad because he's similar to the Enforcer but a lot less effective.
There are a few problems of note, though. The Techomancer is just blatantly better at hacking than the Hacker and the Hacker can't do anything else, so if both of them see play the Hacker's player will be sad. The Face is useless at everything but Facing (and the Technomancer and Hacker are similarly matrix-only), so if they see play you'll want an adventure that makes sure their one trick is useful. The Radical Eco-Shaman and the Street Shaman are very similar characters with a lot of overlap; which one is "better" is debateable but you probably don't want them both in a party.
Another thing you should do is look up and write down stuff like:
What do your spells do? (Make photocopies of them for the players)
What are the total armor values of these characters (Write these down)
What are the stats of this gun/vehicle/drone? Write these down too.
Things really go bad if you start mixing the pregens with characters people actually make; pretty much everyone who sits down and decides to make a face will make one who completely embarrasses the pregen Face and leaves him with nothing to do, for example.
I've been working on a set of premade Archetype characters (more with Missions in mind but usable by anyone), but they are not quite done yet.
