Season 5 of Angel explains mainly what happened to Spike after the collapse of Sunnydale. Angel After the Fall comics follows the events of the season five finale of Angel (Title makes a lot of sense after you watch season 5).
Buffy Season 8 & 9, Angel After the Fall, Spike, Angel and Faith are all comics that continue story-lines from the shows written by the same people who wrote for the TV shows.
I personally haven't read any of them but I did read what happens in them, since I was curious and not a big comic book fan. From what I gather based on what happens and the reviews the comics got I would say there worth reading if you enjoyed the show. Season 8 comics from what I gather kind of went into the fantastical realm comic books allow for, but season 9 comics are being written more like the show was.
Angel: After the Fall -> Spike -> Buffy Season 8 -> Faith & Angel / Buffy Season 9
Is the order in which they should be read from what I gather although I could be wrong. Also Buffy Season 8 comics actually explains something that happens in one of the last few episodes of Angel, it's really a minor thing but if your curious they do explain things and advance the story.
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