These are the best way I can describe the two basic case designs. (At least looking at one aspect of case design). The more aerodynamic style is often found in vintage watches. A very classic design.
The cylinder (ie "water tank") is the way that many contemporary watches are made. The Timex Easy Reader and Weekender models. Most dive watches. Later model field watches. Alan Silberstein. A more "functional" look in many ways.
Which do you prefer?