My first foray into AW was with a Series 2, I didn't have the Series 3 but I believe the case dimensions were very similar if not exact. Series 4 got slimmer and this definitely affected me because my wrists are large. I'm wearing the M/L sport bands on the next to last hole so really no choice for me but the 44 which I'd have gone with anyway. The difference in case dimensions from AW 2 to AW 4 made for a much more comfortable experience. If you are used to wearing watches under 42mm then the 40 is probably good. I like the larger screen size personally because I'm not just looking at the watch to see the time but information. My mother has a 40mm and very small wrists. Screen size on it is still quite good and is a much better fit for her. The displays are significantly improved from S4 on up.