I've got a Rad/Dark/Dark and a Fire/Time/Soul. If you can hit more than 5 targets, Soul Drain provides a stronger buff with double the duration (but double the recharge). I find that I use Soul Drain primarily with Inferno. Because Spirit Drain is ranged and recharges more quickly, I find I use it more frequently. Power Boost is a fantastic power. The best uses with Dark Miasma are to buff Twilight Grasp's heal and Fearsome Stare's -tohit. Dark Consumption is a good utility power if you have endurance issues, but it has a 6 min recharge. I rarely use it (and skipped it for Oppressive Gloom on my Storm/Storm/Dark).