There is more difference in quality between individual clubs within either organization than between IDPA vs. IPSC.
You can go to a poorly run IDPA match, or you can go to a poorly run IPSC match. Beware generalizations about either.
The leadership of your local club is what determines if the match is going to be good or not. My local IDPA club is hardly average in that we usually run 6 stages and our round count is usually over 100 rounds. Our 3 gun matches run around 300 + rounds and 9 or 10 stages. Our attendance is between 30-50 shooters, and we usually run from 9:00-1:00 or 2:00.
But that is because we have a solid crew of folks who work really hard to pull off great matches. The COFs are planned weeks in advance and distributed to other officers for everybody to check for potential problems and bottlenecks. For big matches crews organize and set up the props and target stands the day before.
I know of IPSC clubs who run the same way. Tight and on the ball.
At the same time I've gone to IDPA matches where I have wanted to strangle the match director to death.
Personally, and this is me putting on my moderator hat for a minute, frankly I get tired of the us vs. them mentality in competition shooting. As was pointed out above, the very best shooters shoot both. Now if somebody who has shot both types for years wants to weigh in on why they like one better than the other, that is perfectly all right. However don't go to one match, at one club, and make a blanket condemnation of the whole sport.
My sport is 3 gun, but I went to a match once that sucked beyond all comprehension. Hours of bottle necks, no written COFs, no rules that made sense, scoring that nobody understood, and a stage that I won thrown out because half of the squads shot it wrong. I left with 2 stages left because frankly I was bored, tired, and hungry.
Now if that had been my first match, I could have thrown down a blanket condemnation on all of 3 gun and never shot another match. Then look at all of the years of fun and entertainment I would have missed.
I've poked fun at IPSC guys (usually about your spandex running shorts and coat hanger style holsters
) but in reality some of the best shooters I have ever seen or gone up against have been IPSC guys who have absolutely WHOOPED the pants off of me. My philosophy is that if they can whoop me, I best not make to much fun, they might just know something I don't.