For a budget build go with the 750k, it will be fine. As for the case, the HAF 912 has the support for the ATX mobos and generally good airflow.
Admittedly the mini has the better looks. However it should be fine, you can get good enough micro ATX mobos anyway if you want to upgrade at some point.
So both are good choices. I would still probably side with the HAF912. And offer another choice with the Antec 302.