Devstack is probably the oldest OpenStack deployment tool. It was created to automatically spin up clouds in the OpenStack CI environment, and for OpenStack developers to run their own tests. By now, many use it for training, proof-of-concept and personal education.
A Devstack cloud is deployed by a huge shell script which takes the software directly from OpenStack's Git repos. While you can create a bleeding-edge cloud, you can also select stable versions of OpenStack.
I don't know Microstack but suppose it's a more polished product, with better user-friendliness. Devstack is a bit rough. On the other hand, from the description Microstack seems to be a bit shrink-wrapped with much less configuration options than Devstack.
One detail that has hit many users: Devstack doesn't care for persistence. After a reboot, the Devstack cloud is not in a usable state (though it can be put into a usable state if you know how). You will find plenty of questions regarding this on the old ask.openstack.org site. I don't know if Microstack is better.
Packstack is another deployment option. It only runs on Centos, and it requires at least 16GB RAM (about 8GB for Devstack), but it is easier to use and perhaps more stable than Devstack.