you should probably watch the whole HXH-TV first, since that's where it starts.
Then go OVA1, which is basically eps 63-70 of HXH tv.
Then Greed Island, which is eps 71-78 of HXH tv.
Then GI-Final, which is eps 79+ [img]i/expressions/face-icon-small-tongue.gif[/img].

Clear?