[CanRay]

Mastermind, Hitter, Hacker, Grifter, Thief.

[The_Gun_Nut]

Five is a really comfortable number, but I often run groups of six people.  I've run solo games as well (my in/famous martial arts game played with Ninjas and Superspies/Mystic China), and also games of a dozen people or so.  Six is my comfort limit, as my attention tends to get spread too thinly.

However, I have found that if you approach a large group of players (6+) and let them know beforehand that you will focus on different players for different games, and that they will all get a turn in the spotlight, then the game goes a lot smoother.  An odd case in point, the martial arts game that started with one player, ran solo for several games.  When we started adding people in, I let them know that this was the original solo player's story, and it will focus on him for the most part.  Everyone got some spotlight, but it was centered around the shaolin monk and his eventual ascension to enlightened immortality.

Used the questionable Palladium rules system, but the game remains one of my favorites to this day.

[Angelone]

I like 6-8 it usually gives a good spread of archetypes and won't bring the game to a halt if 1 or 2 players don't show up.

[The Seven]

Four, on my games. A razor/gilette, a caster, a secondary razor/gilette (or maybe an adept) and a face-or-hacker-or-rigger. Always seems to work fine.

[Exodus]

Mastermind, Hitter, Hacker, Grifter, Thief.

Somebody watches Leverage. 
I'm currently running a 2 man game of semi-newbs, 1 punchy adept and a technomancer, they were my first shadowrun game experience and I theirs. (Yes, I jumped straight into gamemastering, I'd like to try SR as a player but I'm picky about my GMs)
I'm about to combine that campaign with another I'm running with 3 folks. 1 newb and 2 SR3 novices. I just need to do a very technomancer-centric run to teach the techno what he's capable of and then tie things together on the storyline side of things and we'll be set.

[Sichr]

I usualy GM 6-8 group of people. We had a times when there was 9 players actualy at the table and another 2 via Skype..that was a hell but we had done well. Funniest thing was when I used projector and have those online players videostreamed at the top of tactical map and pictures I used for the atmosphere.

Whenever it happens again, I would split them to more teams. And talk mainly with leaders/representatives they chose.

[Glyph]

When you are gaming online, it is easier to focus on one player without neglecting the others.  But the biggest downside to online gaming is that, unless the group is separated doing their individual things, you are stuck at the speed of the slowest poster.  This can be frustrating if you are trying to get through a combat and one guy is only posting once a week, especially if everyone else is capable of doing daily posts.  The other thing is that you are likelier to have 2 or 3 players simply drop out altogether at some point.

So for online games, I would recommend starting out with a larger pool of players, and expect to lose a few of them early in the game (or sometimes even before the game starts).  Have a reserve player list, maybe, and have some strict posting guidelines - let people know that you will NPC their character if they are holding up a scene, or kill off their character if they don't post within decent intervals.  Because that's the biggest game-killer that I have seen online, and it is tragic because usually there will be a few players who would have kept going if one or two players hadn't bogged down the game.

[WyrdNyrd]

I'm planning a new campaign with three people. The exception I am making though is that they will be able to create two characters so I'll have a total of six PCs.

There are rules for the characters too:
They have to be different personas.
No relations between the characters (Family, friend or other).
Cannot pool resources during creation.

I'm doing a high power campaign and I want to offer some flexibility with character creation with the low amount of people I have. I believe this will give them great opportunities to try things they otherwise wouldn't with only one character.

[Blond Goth Girl]

Six is perfect for my GM'ing plus couch space and player preference.  Since we only game twice a month and are schedule masters, most every game I have six.

I blog some insights if anyone cares to look.

http://www.penandpapergames.com/forums/blog.php/2735-Blond-Gamer-Girl

[mortonstromgal]

3-5 is ideal, potentially you can do 2 in 4e though starting characters should be 750BP rather than 400BP to make up for their lack of numbers.

[Icarus]

In my experience, 4 - 5 + GM is usually best. Less can be a kind of lacking group, while more tends to be hard to control. We once (in a different game) had a 13 player group, which was terrible, it'd be like an hour between people's turns.

[DesVoeux]

I prefer from three to six players when I'm GMing.

On the low end, with three players it's much easier to keep them focused and let them each have their moment in the spotlight. The bad news is you're going to have to use NPCs to assist the players more, unless they're higher level or the run is simpler. (A three-man team of a street samurai, hacker/technomancer, and mage can do pretty much everything if they have the skills.)

On the high end, with six players you're pretty much guaranteed to have a player for any given scenario and, as a result, the players are usually much more comfortable in specializing. Faces, riggers, CQC specialists, and even hackers are much more common when you have larger groups. The bad news is that it's a pain to get everyone to focus, for the team to agree on courses of action, and for the GM to keep track of everyone. It's also harder to give everyone their moment of glory, and the games take longer.

(Four or five players is, obviously, the happy middle ground.)

[Coldbringer]

In an ideal world 4 to 5 players is perfect. In my current game I am at 3 players its working well, although they are magic heavy and  a bit NPC dependent at times. I have done a couple of 2 person runs with part of the group that went well.

[Canticle]

Three person runs work alright, but four is the best number for rpgs. It just works.

[Morg]

I find that it really depends on your group of players some 3 PC groups were calamitous and would only last 3 sessions before I wanted to Kill all the Players (not the characters) ware as I ran a 16 player game for 2 years without a hitch and everyone had a blast later they had to split in to 2 groups of 6 and one of 4 and that is what I run now sadly we lost out on some of the day in the life of sessions it is still great to get them all together from time to time hand the 3 teams the same Run but with different objectives, this is where having a tablet with an auto roll program helps, I hand all of them the mission objectives on 3 different flash drives and let them at it.

It dose require a bit of maturity to handle PVP shadowrun and not metagame but thus far everyone is understanding and no ones feelings have gotten trashed