The Sebo Automatic X4 is a staple in the high-end vacuum market.  The no-nonsense design from the German outfit makes vacuuming a breeze.  This machine is designed to change its height adjustment on the fly.  It does so by detecting the amount of resistance on the brushroll, then moving the nozzle up or down depending on the floor.  This vacuum can easily do bare floor and carpets of all length.  With inexpensive parts, filters, and bags this machine is well worth the price as they pretty consistently last 20 years under normal use.