As has been repeatedly stated, both are great. Flat is great for licking, teasing, and to lovingly bully with boob envy. Big milkers are for squeezing, titfucking, and sleeping on. That said, if I had to choose one or the other I'd go for shapely big ones, because paizuri is one of my main fetishes.
Speaking of, why is there no proper tag to look for the opposite of pearl necklacing. I want to fucking cream-pai those soft pillows, not poke the most sensitive part of my dick out of the fluffy heaven just to cream her face. Especially with a tight blouse like the first pic in the post above this, you unbutton it just enough to slip in there, ride her till your balls are empty, and then button her back up so she can walk around all day with the smell of your spunk right below her nose.