We have also found their support and general attitude towards us (as a long term customer) getting worse recently, so much so that we are migrating off their platform.
I have no experience with compose.io, but will recommend object rocket / rackspace for mongo hosting. Great support, reasonable prices (as reasonable as mongo can be)
Who are you migrating to? I've been happy with Mongodirector (scalegrid)
We use MongoDirector for our production Mongo instances and it's been great. No issues since we switched to them in September 2014.
Self hosting on AWS. The new MMS makes it pretty painless... clustering, backups, alerting etc, better IOPS and about a third of the price of compose.
Same offer for you! I'm happy to talk over email. I'm sad you're migrating away.