Well I think we may have to agree to disagree here. Just a few more points.
Grappling requires an attack vs. touch AC, then a grapple check. Stunning fist requires an attack vs regular AC, then a fort save. Clearly grappling is easier. Also, if the GM is optimizing the wizards, I find it more likely that he would optimize their fort save more than their grapple.
I guess we will have to. However, I'd like to state this another way: "Stunning Fist requires a fortitude save." You choose to use it after you hit, so anything that happens prior to choosing to use it is irrelevant. It costs no action, it's purely an extra topping on the kung fu sundae. You also neglect to mention that grappling someone else leaves the grappler vulnerable. Stunning someone doesn't inconvenience the stunner in the slightest bit. And yes, fortitude is a tough save to beat, but at least the DC rises with level, unlike spell DCs. And the thing with grapple is, it's not an incremental set of conditions. Oftentimes, it either works or it doesn't. As my friend puts it, "it has no setting between high and off." If it works, and you're optimized ot grapple, you can probably dominate. But if the enemy has grapple countermeasures prepared, it won't do much if anything. And because of it utterly dominating in the former case, eventually anyone afraid of that happening will find it worth it economically to get protected. Someone can have a +50 fortitude save and still roll a 1 (or alternatively, if you want to bring up Mind Over Body maneuver, you can just use stunning fist after they've already exhausted their immediate action for the round). Someone with Freedom of Movement? There's no chance of beating that, other than a dispel magic. Like I said, grapple works good in the early levels, when mages aren't much of a threat anyway, which...kind of negates the importance of being good at "mage slaying." Right around the time magic starts dominating martial -- level 6+, generally, is when the anti-grapple measures have become plentiful and easy to obtain.
If you encounter an enemy with a low enough AC and fort save, you can use shuriken and poison.
You can do some good stuff when you have a grappling advantage. Stunning fist opens up no further combat options.
You can grapple all day, stunning fist has a number of allowed per day uses.
The +4 grapple bonus from improved grapple is useful defensively against one of the more annoying monster tactics.
If you want to further powergame grappling, you can use enlarge person and the half-vampire template.
All true. But like I said, the more splat books you add, the sooner and easier it is to make grappling obsolete, at least on the targets you most want to go hug. The closer to core-only you get, the less likely there's even enough "important" feats available that a monk really can't afford to spend one to pick up Imp. Grapple and get Stunning Fist via class. Really, what amazing, must-have monk feats are there in core? The only one I can think of is Imp. Natural Attack (unarmed strike).
If you really think Stunning Fist is useless, then yeah, there's not much reason to take it over Imp. Grapple, obviously. But, if you think it'd be even slightly useful to have, there's no logical reason to ever take Imp. Grapple via class and then have to wait until mid levels to pick up Stunning Fist. That was all I was saying originally. I don't know why it turned into such a big debate. Because I assumed Stunning Fist would be useful to a straight classed monk? Hell, even if you're making a grapple monkey, you can grapple, punch, AND stun a guy if you want. That works well, too. Stunning and then grappling would be a nice combo during a flurry of blows.
