Well, from my perspective, although im an IT guy, i would prefer to avoid 'building' it , since i havent had a desktop for almost 10 years until recently :D. It makes sense to build it if the price difference is around 15%-20% less than taking it as a whole.

However, my biggest issue with building it is the warranty. If you are building it, it means ordering pieces from multiple shops, most likely ordering from eshops or shops that arent exactly in your neighborhood. In case of an issue, how much you value your time to go and return, communicate/find a solution? I would expect that in this case, for every person this has different value, depending on location and personality.

I wont say what is better, since as i mentioned depends on what needs and priorities each person has, but i will say what i did in my case and i think will follow up in future. I try to buy tower and motherboard together, from the same shop. If i can find a good PSU there,even better! Rest of the components i can 'afford' to look for them somewhere else. But thats only my style though.