Rich: Both is better -- MPPT and tracking complement each other perfectly. Tracking pays off in the summer, adding 3-4 hours of charging time per day over fixed mounts. MPPT is great in northern climates in winter, when cold PV panels make waaaay over faceplate voltage. For instance, here's my Outback solar controller this morning (this demo would be more impressive if I knocked all the snow off the panels
):
The nominal 24V panels are making 34VDC
at the controller, while the batts are cruising along at 26V. Electrons flow downhill, but you only need a little gradient -- like 1 volt. The rest of that excess voltage is wasted, burned away as heat at the controller or in the battery. An MPPT controller tracks the battery voltage, down-converts the panel voltage to just a bit higher, and turns the excess volts into Amps. The panels are making 27.5 A, but 33.7 A are going into the batts. That's a 22.5% increase, even with nearly-full batts. It can be a 30% gain when grid-tied or when your cells are thirsty.