The Heph C is the ultimate command unit IMHO. Speedy, decent armor and packs C3 BHP AND AECM. Not only can you share C3 coverage with all your allies, you also give blacket ECM coverage to anyone nearby. Bonus points that narcs will not stick if they hit something in an AECM field.
Of course the downside is you'd probably have more firepower if you mounted a sling shot on the turret, but you can't have your cake and eat it too.
Hmm interesting, I'll have to look into that.
And the trick in command roles is to be agressive, but cautious. Don't die, in other words and always have escape plans if you get ambushed.
Atlas E "Master and Commander" mech is obviously the goal to shoot for. Equipped the C3 and GECM along with extended sensors, LRM's and PPC's make him an excellellent command mech.
The Raven with the Narc's and just about every sensor suit under the sun is a great starting mech too (though you'll need a little bit extra cash than what you start with to buy it, usually people at the beginning are willing to part with their 3-5k left over at the beginning). It's armament isn't bad either - I've taken out Uziels with it, and it's pretty great for dealing constant damage to someone when they are distracted by a bigger nastier mech near you.
Trick is, never make yourself known and "on the front lines". As a command unit, you are not a brawler, nor are you a long range specialist. You need to be in the action, but on the side lines. Stick with teammates preferably while finding unique angles to scout ahead from by flanking the enemy and dealing support damage (but not to the point where you are on your own completely).
Scouting solo in a command mech works, especially with the C3, but it's much riskier and puts you at a greater risk. This is okay to do on maps like Kagoshima or Palisides which offer many escape routes for cover (which the raven excells at getting to), but on maps like death valley you are toast. It's better off on those maps to stick close to bases, or stick close to allies.
I've had good success doing a commander role. One game I was top of the scoreboard with zero deaths and 5 kills while the player just under me had 11 kills and about 5 deaths or so. The secret is to really not die and play cautiously. You don't focus on kills, instead you focus on supporting your team in any way possible. If that means dealing lots of damage with teammates while taking care to not be the focus, or if it means you are parked on a hill scouting and hitting with LRMS as your team advances, or simply means running around everywhere at max speed dodging shots then that's what you do.
Commander roles are more about being that intel and damage support in any way you can, rather than playing to a specific "combat role". Basically, adapt to the situation to accomplish the goals using a "command" vehicle.
EDIT: And don't be afraid to ask for cbills, especially by stating you'll be using a mech with C3/narc. Teammates LOVE C3/narc mechs so people will generally scrounge up change twoards a player who wants to get one. It was how I was able to get the Atlas E in the previously mentioned game that allowed me to really get a good score.