Well the Model 29 is THE Quintessential, Iconic Smith and Wesson Revolver.
There are several Iconic Smith & Wesson Revolvers, but the 29 is at the Top of the heap due to John Miluis and Clint Eastwood.
The Model 10, the 19, the 27 and the 66 are right there as well, in terms of being Icons.
Then you have 'Cult' guns that the Collectors go nuts for like the 28, the 57 and the 58.
If your intent is to figure out which one to get first, with the intention of shooting and enjoying, I would steer you towards a used 28-2 first.
Why?
Well even though the 29 is more desirable, the 28 is chambered in 357 Magnum. Ammo in .357 and .38spcl is a little cheaper and a little easier to come by.
Also, the .357 is, in my opinion, the most versatile chambering of any gun out there. Unless you are in Alaska or Africa and need protection from Big Nasty Predators, the .357 will get you where you need to be.
Start out with a 28, shoot 38 specials, and then try out .357 Magnums.
If you like .357s, then you can step up to 44 Magnums.
IF you do go the route of a 29, you can shoot 44 Special through it, and you can shoot those all day long.
Here is my 29 with my 28. The 28 is the 4", the 29 is the 6":