I think what they stress is different.
記憶 is used to stress/emphasize that you still remember something, that you haven't forgotten about it.
昨日の夜は飲み過ぎて、どうやって家に辿り着いたか全く記憶がない。
I drank too much last night and I don't remember how I got home at all.
(I'm sorry that I couldn't think of a better sentence!)
思い出 refers to more of the content of the memory (either good or bad).
高校での一番の思い出は、修学旅行です。
My best memory of high school is the school trip.