I've read all the post TV series Angel and Buffy graphic novels and the Spike ones by far are the best. It really keeps the character alive. I would only advise reading the After The Fall Angel & Spike books before moving onto this to minimize confusion, and if you can get your hands on it Spike: Omnibus. There are some re-ocurring characters from the Omnibus.
Chronologically if you're looking for post tv series stuff I'd roughly in this order. It doesn't matter so much the order of the Omnibus if you've watched both series, just that you read them.
Buffy: Omnibus 1-7
Angel: Omnibus 1&2
Spike: After the fall
Angel: After the fall (1-4)
Angel: Last Angel in Hell (totally unnecessary all together just as an fyi)
Angel: the End
Angel: Only Human (has to do with Illyria)
Spike: The complete Series
Fray: Future Slayer (anytime at all before reading Buffy season 8)
Buffy: Season 8 (vol 1-8)
Then you can finally move onto the current Stuff, Buffy season 9 & Angel & Faith