TriStar!
The nice thing about a TriStar is that it's bulletproof, idiot-simple technology backed up with superb build quality. The canister is a housing, a fan, a motor, and a switch, period - unlike today's nervous-Nellie, electronically-controlled vacs, there just isn't anything to go wrong. Way before there was HEPA, TriStar was offering quadruple filtration (cloth bag, paper bag, motor filter and after filter); when you use one, there is no vacuum-cleaner smell at all.
Unlike a Filter Queen and some of the other "specialty" vacs, a TriStar is easy to figure out and use, basically like every other canister vac, only better. The TriStar power nozzle on the later CXL, DXL and EX-20 machines is really really good, leaving the carpet fluffy and clean but not leaving harsh grooming marks. I have a cat and a Bissell ProHeat 2X carpet machine, which for most Bissell owners, means that the Bissell pulls up a lot of pet hair that their vac missed; many new Bissell owners complain about having to pick up ginormous wads of pet hair when they use the cleaner. I didn't have that problem at all, even with a tuxedo cat on ivory carpet.
I second the statement that you need to get one of the older, IEC-built machines based on the Compact design, not one of the new MG-series machines. The new machines don't have the Ametek motor, and while the canister housing is still magnesium alloy, there's an awful lot of plastic used for wands and the PN. And the price is very high for a new one - I understand that list price is about $2600.
Figure about $400 to buy a decent CXL or later Compact-style machine and put it into really good shape with the complete selection of tools. I have never repeat never repeat never seen a Compact-style TriStar offered on eBay that was complete and correct.
P.S.: Bill, I've been trying to email you, but it keeps bouncing. Any idea what's up?