They're both underrated by fans, especially A Feast For Crows
which only has a few pacing problems, and is largely excellent. I'd rate it above the original A Game of Thrones
book, actually. I think a few of the Dorne and Ironborn chapters could have been merged, and the early Brienne chapters are too slow, but other than that it's a masterful book.
For all it's huge faults A Dance With Dragons
is also kinda underrated by fans as all the non-Essos stuff is really good, and I like the Arya and Victarion plots in Essos a great deal. My major gripes with that book are almost entirely to do with Tyrion and Dany's plotlines (Which take up 22 chapters!) so the sooner those 2 get to Westeros, the sooner the series will be back to the quality it should be. I'm dreading having to deal with Dany spending elongated amounts of time with the Dothraki, I'm seemingly the only fan that couldn't case less about them. Uninteresting savages.