Hi LabGuy, thank you for the referral! What I'd recommend depends on application, but as a general answer:
For an electric (slow speed) handpiece, the Ultimate XL from NSK is probably the best intersection of quality and price. That's what we recommend and sell the most of. Parts are readily available and are not too expensive, and it's a brushless model so it gives you the option of higher RPMs as well as increased torque. If price isn't a consideration, then Kavo, but parts and repairs are considerably more expensive. They've got three solid options for handpieces.
For a brushed handpiece (and if you don't do a lot of heavy grinding, then there's no reason to pay extra for a brushless),the Volvere i7 from NSK is reliable and has good dust seals, and also the UG33 (used to be sold under the Brasseler label but is still available). Those handpieces have universal cords, so you can use them on almost any control box that accepts brushed handpieces.
For high speeds, the Bien Air TD783 (or TD890 for water) has the most robust bearings/higher torque, and seems to stand up better on zirconia. However, you have to remember to lube the turbine, which makes it a no-go for a lot of people. Second up then would be the NSK Presto or Presto Aqua, which have the lube-free bearings that most people seem to prefer. Zirconia is just tough on all these turbines; people tend to press down harder on zirconia for some reason, so there are more early chuck and bearing failures across the board.