Personal preference is involved to some extent. I generally prefer to go with air cooling whenever possible, but if I go with water I tend to build full custom loops. The latter would have the best performance, of course.
Since you appear to be building a rig for work, I would think that reliability would be paramount. At stock speeds even the air cooler I linked is more than enough for adequate cooling of an i7-8700K. Even with a mild OC (e.g. MCE enabled to hit 4.7GHz all cores).
If you are overclocking, you may consider better cooling options. A high end air cooler will match or beat most <=240mm AIOs while costing less, so there is also that consideration. The case you have selected doesn't appear to support radiators >240mm so the suggestion of a larger AIO would either require modifications to the case or a different case altogether.
Yes I'm trying to build a rig for work Photoshop, video editing, etc. Never been big into overclocking. Had a Citrix chip way back in the mid 90's that I overclocked. Had a friend that was into gaming and tweaking the clock speed. I liked how well his gaming computer ran so built one with the same motherboard and CPU as his.
Speed is very important to me but I do not want to risk reliability. If the computer gets unstable and crashes during the long render, or a complex Photoshop operation, then all the speed is worthless. And I really don't feel like doing a bunch of custom water cooling to get overclocking. I have a water CPU cooler in my rig that I am running right now. (I7-3930K) At the time I bought that CPU that cooler was the only option. Intel liquid cooled thermal protection for LGA 2011.
I can happily run an air cooler if that is adequate for this system.
Any opinion which of those motherboards would be better?
Does anybody on this thread have the 8700K with the Optane SSD 900P? Curious if that is as fast at it seems it would be?