Amps on top?

I depends on system configuration.

Integrated amp on top so you can read the dials and adjust the knobs.

or

Power amp on the bottom (or a dedicated stand) because it's heavy and to make the speaker cables shorter. It doesn't have anything to read or adjust.

Yes, it’s nice to have the weight low in a rack, helps stabilize, and avoids a high fulcrum point when up top. Especially with flexible wood floors like mine. Perfectly level is your friend when weight is high.

I have my heavy amp and my heavy R2R deck on two separate cabinets to the left and right of the equipment rack for several reasons. AND felt on the bottom of the cabinets so I can spin the cabinets individually to access jacks/cables.

If you look at my virtual system

https://www.audiogon.com/systems/9511

I made a ’ventilated stand’ to put the preamp on that cabinet below the amp, so I can easily get to it’s rear.

https://www.audiogon.com/systems/9703

whatever is on the bottom can be removed without having to move the heavy amp above. I sized the inside clearance for many/most McIntosh pieces and made the stand hold 100 lbs. for big McIntosh/Other heavy amps.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

While viewing anyone's system, if you click on full screen (top right corner), you will see any captions that are otherwise obscured.

I'm here for the audiophool reason 

On top isn't the point, having space and air for cooling is the big deal. If the amp is on top, it has the space and air for ventilation. 

Amps close to the ground,  even my GaN Monoblock's and they weigh nothing compared to my Class A power amps.