(It just occurred to me that all three of the Feds mentioned above wrote [lied?] about their service in Arkansas. Does that mean anything? Was there something in the water? I don't know.)
On the Confederate side, Joe Johnston was by far the least reliable memoirist--his book is a tissue of lies from start to finish--but Hood and Gordon were pretty bad as well and Longstreet was his own special case. Lower down the food chain is Henry Douglas' memoir, I Rode With Stonewall. It is so self-centered and distorted that historians have joked for years it should have been titled, Stonewall Rode With Me.
On the other hand, some memoirs are first-rate. Richard Taylor's may be the best of the bunch.
I was always told by my betters in the history business that the soundest sources are the ones written at the time (diaries, letters, reports), and after plugging away at this stuff for nearly forty years I am convinced that is true. We can't do without memoirs, of course, including Porter's, but it pays to be cautious.
Sorry for the long-winded lecture. Occupational hazard.