which type of confiuration would yield the best recoil compensation?

Depends on the frame, every weapon type has different mount options.

pistol: I'd say custom grip, at around 100 nuyen, you cover all your recoil.

For SMG/Machine Pistol: grip and a gas-vent system and if available shock pads on the detachable stock.

Shotgun: grip, shockpads and if available underbarrel weight

Rifle: Shock Pads

Assault Rifle/LMG: vent, grip, pads, barrel weight or bipod depends on your mobility needs

MMG/HMG: Grip, Vent and harness or tripod depending on mobility needs

Rotary: Grip, and harness/tripod/vehicle mount based on mobility needs

Custom Grip isn't yet definied in SR4.

If I remember right, heavy barrel worked without taking a mount. You could then use an under-barrel weight as well.

Definitely foregrips on SMGs and MPs, with gas vent. Most folks don't take the time to unfold the stock, so stock/pads wouldn't help.

Shock pads are a no brainer on any fixed stock. Custom grips are an easy point too, unless you're group shares weapons or throws them away regularly.

For an MMG or larger, I would go with gas vent, foregrip, and the harness.

Does anybody's group ditch their weapons after they've been used, especially when a death has resulted? With ballistics testing what it is, I would hate to spend a few K to upgrade my piece, only to have to toss it because Lone Star got hold of a bullet...

You don't have to throw away the costy electronics if you want another barrel...

How much RC would a grip give?

It was -1 RC, IIRC.

Under the current ruleset, gas vent (for any automatic) and shock pads (for any rigid-stocked weapon) or folding stocks (for smaller, more concealable weapons) are the basics of any recoil comp arrangement.

If you aren't worried about concealability or size, a gyro-harness is one of the ultimate compensation techniques. Not subtle at all, but you can now fire (and move) without nearly the penalties. Combined with venting and a shock pad, you'll most likely be able to chew away on full auto at no penalties.

If you've got a cyberarm, a cyberarm gyro is another 3 points of RC for free. One of those pieces of cyberwear that really raises eyebrows if it gets spotted, but letting you get 3 more rounds a turn out before worrying about recoil is stupidly handy if you want to chew up a target.

Tripods fit into sort of the same role as the gyro harness, except they're less mobile (and less expensive, if memory serves). You can't move around with them nearly as easily, but once deployed, you've got a truly stupid amount of recoil compensation at your fingertips.

Bipods are one of the more overlooked types of recoil compensation. While you can't just open up and get the compensation like you would with some of the earlier types, finding a solid enough object to plonk the weapon down on (I'd call it a Simple Action) isn't hard... the hood of the car you're behind, the ground you're prone on, the edge of a windowsill or a building's roof. The other nice thing about bipods is that you can use suppressed weapons on automatic without racking up the penalties. One of the favored custom builds was a scoped, suppressed, bipodded and shock-padded assault rifle, giving you enough reach for short-range sniping, enough compensation to contribute some lead to a firefight (or hit an unaware target with a burst, to make sure he stays down), the suppression to reduce the enemy's awareness that you're there, and the full-auto position on the selector for when you need suppressive fire. Under the current RAW, the Ares Alpha's built-in 2 points of recoil compensation would help out here, as well (giving you 5 points with the bipod in place). Also under the current RAW, suppressors and gas vents are compatible as long as at least one of them came with the gun, but I house-rule around that (one vents gas, the other contains it... only one can be effective at a time).