I like the tactic with hellpower and spawning horrors while blood mages are immortal
Other Ulm themes are pretty weak but BF is one of my favourites too and it turned out not that weak once in a MP game its the most versatile ulm theme too.
well, i go for LA Ulm, MA Ryleh and EA Mitclan. But Ashen Empire will always be my favourite for nostalgic reasions.