Was Joss Wheadon involved in the post-show comics? That wholly determines my interest in them. That it sprung from the same creative mind as the show.
Yes, it was produced by Whedon and he wrote/co-wrote a lot of the storylines and individual books. And it is considered "canon". Same for Season 9 and 10 series of the comics. In later stories they also start including Angel storylines and characters.
There are some lists around that list all the official comicbooks and preferred reading order. But I would say that starting to read Season 9 would be pretty good starting point. And if it interests you, then digging up rest of the books and order in which to read them.