Last month we learned that Garmin was using a MediaTek (MTK) chipset in its new eTrex H-series. I'm currently testing an eTrex Legend HCx and decided to put it up against the SiRFstar III chip in my trusty 60CSx.
With a new baby in the house, I couldn't get away for a long trek, nor could I record tracks over multiple days, so this isn't the most scientific test possible. Fortunately, I live near redwoods, which are dense enough that stray track points occur frequently and lesser receivers will often lose their satellite lock. This made for an ideal testing ground.
The tracks below were collected on mountain bike. The two GPS receivers were placed in the backside mesh pocket of a CamelBak hydration pack. The trip was an out and back (except for one loop near the middle of the ride) and the units were placed on opposite sides of the mesh pocket. This way, one unit got more of a southern and western exposure on the trip out and a northern and eastern exposure on the return trip. And vice versa for the other unit.
This trail zigs and zags a lot, especially at first, as you can see below. With rare exceptions, the entire trip is under moderate to dense canopy. There are no published trail maps of the area so, even if such maps were accurate (and trail maps often are not), there is nothing to compare the tracks to except each other.
The portion of the ride nearest the trail head is shown below. Click the map for a larger scale image. Interpretation follows below the thumbnail.
The Garmin 60CSx's SiRFstar III chipset is shown in blue, while the Legend HCx / MediaTek chipset is shown in red. The yellow arrows above show a stray track point collected by the 60CSx, followed by a couple collected by the Legend HCx.
The pink arrows, above and below, indicate where both receivers seemed to be a little wide of the mark. The map below shows the second half of the ride.
This is just one sample, and the only thing to compare are the tracks of these two units recorded in two different directions. Still, there seems to be little difference between them, at least in this test. I remember my old pre-SiRFstar III receivers and the problems I had getting and maintaining a fix in the redwoods. I think that either of these units will serve you well and, in my opinion, any purchasing decision should be made on the basis of features, not the brand of chipset.