Cablevision: zero HD.
Verizon (FIOS) and Comcast: almost half NOT HD.
Check carefully before you subscribe. After subscribing, your provider may make it very difficult, if not impossible, to cancel.
MLB.TV is the Internet version, which can run on a Roku box or other devices connected to an HD TV. Also, computer, tablet. Check whether it runs in Google's Chrome browser. All games should be in HD. However, the experience may not be like TV, switching quickly and fast forwarding with some precision. This may differ among devices.
To get around the local team blackout, consider with caution: unlocator.com or purevpn.com. Not for the faint of heart.