Obviously this isn't a 1-to-1 comparison because they have a different comp for both kills, but Nezyt appears to have been both Destro and Demo for kills:
http://worldoflogs.com/reports/g8eyt...=10707&e=11333 (Demo)
http://worldoflogs.com/reports/g8eyt...=10707&e=11333 (Destro)
For him he did a larger portion of the damage to them as Destro.
Now, for my personal opinion it depends on strat/comp. If your balls are going to be spread out and not gripped in by a DK every time (Wee 10H) then you'll be better off as Destro + MF than Demo.
If your strat depends on DKs gripping them in for fast AoE while they're all clumped, Demo will be better for the burst AoE aspect.