Summer brewing means warmer tap water, which means that my immersion chiller can only cool the wort to about 75 degrees. I typically cool the wort to 68 degrees before pitching. I have a fermentation chiller that will cool the wort by about one degree per hour.
Would it be better to pitch at the higher temperature, then cool the wort and yeast over the next 8 hours or so, or would it be better to cool the wort to 68 degrees with no yeast, then add the yeast about 8 hours later?
On several occasions I have cooled with my IC the best I could say to 75F in the summer. Then I put the wort in my fermentation fridge until ti gets to 68F or 65F, for example. I usually don't wait for it to happen I just let it go overnight. Then I pitch the next morning. It could be 8-12 hours later.
As long as your sanitation is spot on there won't be a problem waiting to pitch if you are still actively trying to cool the wort.
Pitching at fermentation temps, or slightly below your desired fermentation temp, is becoming the standard best practice I believe. And it works for me.
Also as the yeast are trying to become active, a drop in temperature tells them that the environment is changing in a way where they might want to become dormant. Some strains are more sensitive to that drop than others. Another reason why its best to pitch at fermentation temp or slightly below it.
The first 72 hours after pitching the yeast are the most critical in terms of flavor development. If the wort is too warm during that period, you can develop off flavors. It is much better to cool the wort before pitching (using your usual excellent sanitation procedures) than to pitch and then cool it down. I have my own sorry experience to back that up!
My immersion chiller doesn't get me much below 72 in the summer, so I chill it down to whatever temperature I want to get to by immersing the kettle in an ice bath to help things along while the chiller does its part (I have a large "cube" cooler that the kettle fits into very well).
Also, for many yeast strains there are good reasons to get down well below 68 to start fermentation. I recently brewed a Kölsch where the optimal temperature range is around 58-60, and it's important to pitch close to that range if you mean to keep things there for a couple of weeks.
I guess what I'm saying is it depends on the yeast you're using. With strains like US-05 I've never had a problem pitching in the 72-74 range and lowering fermentation to below 68 within a day or so.