Thinking about buying one as a birthday present for my wife. I'd probably buy the series 6. I'd buy the SE except I think she'd really prefer the always on face. She has an old Garmin that she likes to use to track her runs but it seems to be struggling to maintain accurate gps tracking. Are the Apple watches accurate for timing and tracking things like runs, hikes, bike rides, etc.? Are the heart rate monitors accurate? I know the pulse ox seems to be problematic at this point. I'm thinking the smaller watch would be the better option? I'd especially like to hear from women whether they prefer the 40 or 44 mm watches. Thanks.