I remember somebody whose competence I rate highly talking about ending up picking Cassandra over Riak (at a point where Riak was technically decently mature) simply because of availability of ops expertise - basically his take seemed to be that Basho support was solid but they hadn't succeeded at cultivating people he could *hire* to handle as much as possible in house before calling in the gurus.
(I can't, of course, speak to the truth of this, only that over a couple decades of knowing the dude in question and working with him on and off he had sufficient Clue that I expect he did put in the effort before coming to that conclusion)
Though it had a couple years head start when there really no other options for people wanting that kind of kit.