Agi is the best for tanking group pve since they will just parry your attacks and you won't deal any dmg anyway.
Do not use lifesteal (or fiery) unless you have high amounts of hit rating, the proc itself will miss most of the time if you don't. Works great for soloes when combined with hit rating and can restore some hp when grp pveing. Remember that some mobs will resist parts of the dmg or even the entire proc and the healing is based on the dmg dealt so LS loses a lot of its power (sometimes all) if the target has high shadow resist.
Unholy is great because the proc never miss like LS and the dmg can't be resisted. Mobs in duskwood who fully resisted LS took full dmg from unholy making it the strongest dps enchant. The debuff is hindered greatly by avoidance wich is sad but it still helps quite a bit. Several twinks can apply several stacks of it. (It obviously isn't shadow dmg. The tooltip is bad in so many ways, why trust it at all?)
Tanking in grp: agi + pouch/ DW agi. Switch pouch for agi when you have lost 100hp, switch back to pouch when getting healed.
Dpsing in grp: Unholy + hitrating. Alternatively LS or fiery if you have the proper buffs and the mob have low resist
Shadowmeld will remove aggro temporarily wich allows you friends to pull the mob away, giving you time to bandage yourself to increase aggro if you are a nelf. You can bandage the tanking twink to full when you are dpsing to increase aggro if you need to take aggro.
Thats pretty much all I know about rogue weapon enchants