What type of chocolate should I use to make a ganache?

I heard it's bittersweet chocolate but will it make the ganache sweet? Is it okay to use milk chocolate? What if you mix milk chocolate and bittersweet chocolate together? I have a bar of chocolate that's 70% cocoa.
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Tags: milk chocolate, bittersweet chocolateRelated posts:
use semi sweet or bittersweet not milk choc. That will make it way too sweet. Mixing milk choc and bittersweet is fine. Make sure you use a double boiler so you don’t burn the chocolate.
Semisweet or bittersweet
http://www.joyofbaking.com/ganache.html
semi sweet is used but you can mix chocolate. The ganache might be a little softer due to the milk chocolate but still be fine.