As with most streaming devices, a lot depends on your net connection.
If you dont have fast broadband you might struggle to watch 1080HD without the annoying buffering problem :/
720 or less might be ok
though legit sources like Netflix and Amazon prime you have a good chance but with Kodi Addons such as SALTS which is one of the most popular, its a little harder.
In cases like p2p streaming it usually comes down to 2 things... firstly how fast the server can pass data to you, and secondly how many other people are watching the same file.
For example....If you watched a new Game of Thrones episode within 24hrs of it being actually being aired, chances are every man and his dog will be trying to watch it too.
to combat this they now have many mirror copies of the same file on many servers but its a bit hit and miss with popular shows/films/events
Live streaming has exactly the same problem.. it may play great if Exeter are playing Bristol City, but when Arsenal play Man United.... *Buffering* :/
a paid for IPTV service can solve this and full sly can be as little as £10-£30 for the whole year. (including box office)
obviously i say that as an example only.... its obviously illegal and would make you feel terrible.
This is why we love satellite TV so much..... it plays great in HD even if your internet is crap and being used by the kids to play FIFA online and watch Youtube videos