Curious about what your concerns with Spark were? I work for a company that supports Spark development, but I don't work closely with that project, so my opinion is not sufficiently well-informed, and obviously biased.

As far as I know, virtually any MapReduce job can be rather trivially translated to Spark's .map() and .reduce() operations. And the downsides are: it's model hasn't yet been proven at the largest scale's MapReduce has been used, and possibly the use of Scala (although Java / Python bindings are obviously available). Were there any other major factors in your hesitance?