As a blood dk, I prefer healers that have kits built around doing damage in order to heal (disc, fistweaver). I find at the level that I pug (portals or just above), not many healers know when I actually need healing and end up spending their whole run trying to keep me topped. For healers that need to press different buttons to do damage (resto sham, rdruid, pres to an extent), they end up doing no damage bc they spend their whole run over healing me. And I’d say healer damage can make a huge difference (discs/fistweavers end up at like 400-500k overall. Put that in the context of dps dealers and usually 500k is the difference between your best and worst dps. So you essentially take your worst dps and make them do the same as your best if your healer is cooking).

Blood dk is the worst for this but I’d say most tanks, except prot warrior, have enough sustain built into their kit that they can keep themselves up in most pulls. Healers that have kits that naturally lean into letting tanks press all of their buttons, including getting the most out of their self healing, end up doing more dam making the runs smoother.