Each has their own advantages and their disadvantages. It all depends on what you want to do with them, and each has their own niche to fill.
9mm is a good choice for personal defense, due, as you say, to the extra rounds. Most people seem to now be choosing the semi-autos for just that fact. Standard loadings are 115 , 124, and 147 grains.
The 357 shines in its ability to handle bullets heavier than that which is custoarily found in 9mm loadings, - the 147 gr bullet is generally the heaviest thing you will fined there, but 357's normally shoot the 158-160 gr bullet at higher velocities than a 9mm will fire a 125. 357's also handle bullet weights of 180 (and some handload even 200) grains.
You can handload very light bullets (normally 100 grains) down to very light velocities in 357 that most semiauto pistols would fire, but not function on. Revolvers do not depend on energy of the load to function reliably.
But the recoil of a full-power 357, though surprising at first, is not too difficult to live with once a person becomes accustomed to it. Barrel length is a factor there, too, as the weight of a longer barrel makes it much easier to shoot and to shoot well, something often lacking in 9mm, especially the shorter and more concealable models.
So it all comes down to what do you want to do with it - personal defense or range-toy. Remember, it all takes practice, whichever way you choose.
