I agree with most ppl that SpellSpeed is not worth it as a heal, neither its cast-time-reduction nor havnt I seen anything in detail concerning how it affects HoTs/DoTs (yes it does, but to what extend is not (yet) known to me :X).

I read somewhere on reddit (forgot to bookmark the thread) that DTR scales quite bad at the moment. So I'll stick with crit.
However this is somewhat of an preference issue, overall I'd say:

Crit>=DTR>>>PIE>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>SpellSpeed