PSU Cases: Top or Bot?

PSU at the bottom is better from a thermal and mechanical viewpoint but depending on case and motherboard layout, it can also be problematic for wiring due to cables either being too short or barely long enough - particularly the ATX12V/EPS 4/8-pin connector.

Since a good PSU is usually one of the heaviest component in a PC, putting it at the bottom lowers the tower's center of mass and makes it more stable as in less likely to get tipped over.
 
I like my PSU on the bottom. My current system has the PSU on the bottom, I dont know if I like it because it is "new" or "novel" or because I feel like it makes my case look cleaner, but I do like it.
 
Hi
Cases with the PSU bottom mounted generally have a grill on the bottom through which the PSU pulls air from the outside and vents it out of the rear of the case.
The advantages of this are that the PSU ventilation is isolated from the rest of the case,leading to a cooler power supply and a cooler interior temperature inside the case.
Top mounted PSU s generally pull air from inside the case which is already warm and venting it outside which will lead the PSU to run slightly warmer.