SE 3, Series 11 or Ultra 3
Apple Watch SE 3 is the one most people should buy. It tracks workouts, sleep and heart rate, runs the same watchOS, takes the same straps, and does everything the Series does for daily use.
Series 11 adds the always-on display - the screen stays readable when your wrist is down, which sounds small and is not - plus the fuller health sensor set, including the ECG app.
Ultra 3 is a different kind of purchase. Titanium case, far longer battery life, a much brighter screen, and features built for open water and long trails. If you do not swim in the sea, hike in the mountains or need the battery, you are paying for capability you will not use.
Case size matters as much as the line. 42mm and 46mm on the Series, 49mm on the Ultra - try one on in Ruwi or Salalah if you can, because photographs do not convey it.