If you could only have one model J frame what model would it be?
I'm probably the wrong person to ask such a question. I have 7 of them at the moment, and wouldn't mind picking up another 2-3 of them.
The "answer" depends on your perceived needs, any personal preferences, and to no small extent how well you've developed and maintained your revolver skills.
A bit recoil sensitive? Look at steel-framed models.
Want square butt or round butt?
Don't mind some recoil and want a more pocketable (pocket holstered) snub, weight-wise, to use as a lawfully carried concealed snub? Look at an Airweight.
Want blue/black finish or stainless?
Want traditional DA, with the ability to shoot either DA or slower, thumb-cocked SA?
Want mostly DA capability, but wouldn't mind occasional SA capability for plinking, sport shooting? Look at the traditional Bodyguard style with the less-snag-prone shrouded hammer (not the newer snub of the same name).
Want DAO? Look at the Centennial-style (or one of the short runs of the 40/42's, with grip safeties).
Want .38 Spl or .357 Magnum?
Want a more durable aluminum frame? Look at the Scandium models?
Want
really light weight? Look at the Ti/Sc/PD models with titanium cylinders and alloy yokes.
Shooter and ammunition considerations abound. Some potential owner maintenance issues, too. (Careful cleaning those titanium cylinders and alloy frames.)
How about a middle-of-the-road lightweight gun, between an Airweight and a Ti/Sc/PD? M&P 340/360 (Want DAO or TDA?). Chambered in Magnum, with black finished stainless cylinders, but still with a Sc aluminum frame, sleeved barrel (steel liner & alloy shroud) and an alloy yoke.
Want one with the ILS (lock) or a No-Lock model?
Fixed sights? Adjustable sights? Night sights? Fiber optic?
Pretty much something for everybody who might want a diminutive 5-shot J-frame.