Ask Slashdot: Which NoSQL Database for New Project?

DorianGre writes: New independent project. Iphones and droids talking to PHP(Symfony) or Ruby/Rails. Each incoming call will be a data element post and I would like to simply write that into the DB for later use. Will need to be able to pull by date or a one of a number of key fields, as well as do trend reporting over time on the totals of a few fields. I would like to start with a NoSQL solution for scaling, but would like something dead simple if possible. Looking at MongoDB, Couchbase, Cassandra/Hadoop and others.