in my experience Xubuntu is the best, I m not using it because is terrible ugly. (KDE is a wonderful modern desktop)
if you will use ubuntu (Kubuntu, Xubuntu, Ubuntu Studio, etc) the most important advice is it:
you can make a simple script like this
#!/bin/bash
clear
echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
take a look at how the µs decreases