Mesos batch system doesn't favor bigger tasks
https://github.com/BD2KGenomics/toil/blob/d08fe8c43d0d18d4d4bdafb9c9c921fd937557bd/src/toil/batchSystems/mesos/batchSystem.py#L298

Sort is ineffective as it sorts by the property descriptor, not the value of the property.

diff --git a/src/toil/batchSystems/mesos/batchSystem.py b/src/toil/batchSystems/mesos/batchSystem.py
index 198f14db..95d565d7 100644
--- a/src/toil/batchSystems/mesos/batchSystem.py
+++ b/src/toil/batchSystems/mesos/batchSystem.py
@@ -295,7 +295,7 @@ class MesosBatchSystem(AbstractBatchSystem, mesos.interface.Scheduler):
         job_types = self.jobQueueList.keys()
         # sorts from largest to smallest core usage
         # TODO: add a size() method to ResourceSummary and use it as the key. Ask me why.
-        job_types.sort(key=lambda resourceRequirement: ResourceRequirement.cores)
+        job_types.sort(key=lambda resourceRequirement: resourceRequirement.cores)
         job_types.reverse()
         return job_types
 
['src/toil/batchSystems/mesos/batchSystem.py']