You might want to compare scheduling between MapReduce version 1 (MRv1) and MRv2, which runs in YARN (Yet Another Resource Negotiator). Scheduler options include FIFO scheduler, Fair Share Scheduler, Capacity Scheduler. In addition to providing scheduler options, there are also many properties that can be configured to achieve very specific scheduling goals.

MRv1 is widely deployed, but MRv2 is picking up and will likely take over. Cloudera will launch Cloudera Express CDH5 (free version) soon - it includes a mature version of MRv2. CDH4 has an earlier version of MRv2 which is useful for experimentation.

Here's a link to the CDH5 beta 2 for download in case you're interested in trying out MRv2:

http://www.cloudera.com/content/support/en/downloads.html