I'm not sure which one I actually live in (you'd think being near the Honor Oak pub would give you a clue, but it takes around the same time to walk to either) - but we find it a great place to live.
Most stuff already mentioned. Like Jane, we use both centres depending on what we want. FH has the library, will have the pool ( my daughter uses Dunstan's for swimming lessons and it's fine - though like a sauna for adults watching). Honor Oak has some nice cafes and lots of playgroupy things going on too.
As everyone has said - great schools (my daughter is at dalmain and we're very happy with it). Nice green space (inc Blythe Hill). And the overground is fabulous. Forest Hill has the lift which is no small consideration when you have a buggy.