If you don't like it, don't reply, scroll on past and get over it. Pretty simple.
You are not obligated to get frustrated and post a response. Granted yes it can be annoying when someone isn't willing to help themselves,
it is a good idea to help teach them the ways. That's what TPU
is about, it's
not about being rude or getting overly frustrated at a very simple help-seeking thread. This forum would not be the best place on the web (in my experience) if it had people replying like this in every help thread.
TPU IS ABOUT HELPING OTHERS, not pissing and moaning that they don't ask questions that meet your expectations...
Onto the OP and his topic, honestly I prefer air just for the sake of serviceability and that even if my fan dies I still have decent cooling due to the airflow of the case. I don't like the AIO watercooling units for my personal rigs, at least yet. Sure I've been tempted, but in my research, my Noctua U14S was on-par with the larger D14 and the H100i, or very close, for less $$$.
It comes down to many things, your case, it's airflow, how you have it setup or modified, are you going to care about noise when the fans ramp up? Are you going to do Push-Pull? Do you want complications and are you ready for them when they occur?
The simplest solution that will still be effective is a good air cooling single-tower solution. Sure the D15 is a beast and will keep your CPU very cool, but it can create access issues to other parts of your board.
There is a lot to think about beyond just the cooling. I would recommend you research both coolers, and look at not just Google as frustratingly suggested above, but also Google Images for pictures where both coolers are installed in similar setups as what you have or plan on using.
As you build your plan and detail it here, we can assist you educating yourself to making the best decision for you. None of us can tell you one is the best...I don't prefer AIO solutions like the H100i, but many do over air. There's more risk with an AIO imho, that makes it not worth it...get at least a H220 system imho. Or better yet, run a few degrees C warmer and run on AIR cooling and have less worries about reliability.
I prefer Negative air pressure because that means that there's more exhaust fans...which leads to air being pulled in from more areas. This provides better cooling in my experience but also creates a dustier case and components to clean more frequently. A positive pressure case will have more intakes, so those areas where are was incoming is now exhausting. This is not as effective at exhausting hot air in MOST situations. It all comes down to case design, component placement, overclocking, ambient (room) temperatures, fan speed, etc.