Linear Tracking Turntables - Best??

The problem with air-bearing arms is that the lateral mass is often a multiple of the vertical mass. So you can be tracking at the right weight for the cartridge, but the lateral mass can cause visible left-right motion in the cantilever. When this happens, the tracking error is significantly higher than that of a radial tracking arm!!

The solution is a cartridge with a lower compliance. This might not work out all the well when it comes to simple tracking, as the vertical component (mechanical resonance) might not be satisfied. 

I used to run a heavily modified Rabco arm many years ago that got around these problems- but then had other problems, most notably mechanical resonance in the track in which the arm ran. I do think linear tracking is the way to go, but have yet to see an embodiment that solves all the engineering problems.

My Trans-Fi arm can taken away from me only over my dead body.

The much higher effective mass in the horizontal plane of most linear tracking arms might not necessarily be a disadvantage.  Bass is typically mastered monophonically, which means only lateral movement of the stylus tracing the groove.  The higher effective mass in the horizontal plane would keep the arm from moving so easily so that all of that bass information is imparted to moving the cantilever which means that all of the bass information is actually recovered by the cartridge.  This is the principle behind the Moerch anisotrophic tonearm.  I don't know if this is also what is behind the sound of certain linear arms, but, it might be the case.  With arms like the Walker and Mapenoll, I heard really deep and powerful bass.  

Of course the higher horizontal effective mass would be bad news with off-center records which could severely stress the cantilever.

Does anyone have experience with the Shroeder linear tracking arm?    

One cartridge that plays into atmasphere's point about the lateral versus vertical mass of air-bearing arms is the Decca/London's. The current Londons have a vertical compliance of 15 but a lateral of only 10, making them a good candidate for an a-b arm, at least in regards to effective mass/compliance.

@larryi, there is a problem with this statement:

 Bass is typically mastered monophonically, which means only lateral movement of the stylus tracing the groove.  The higher effective mass in the horizontal plane would keep the arm from moving so easily so that all of that bass information is imparted to moving the cantilever which means that all of the bass information is actually recovered by the cartridge.

The problem is that bass is not mastered monophonically! Its mastered in stereo like everything else. Dealing with out-of phase bass is a problem in modern recordings, which is why a lot of mastering houses employ a passive device that makes the bass mono for a few milliseconds until the out of phase bass problem has passed. We have such a device in our mastering suite, but prefer not to use it; so far anyway I've found that if you just spend a little more time with a mastering project and do some test cuts, you can sort out a way around the out of phase bass without resorting to processing, which I like to avoid.

Further, the higher lateral mass simply means that the arm can be moving one way while the cantilever is going the other way. I've seen this in air-bearing arms with cartridges that are too compliant, and in one case at a local dealer's shop (House of High Fidelity of St. Paul, no longer in business) the excess motion resulted in the cartridge body shedding the cantilever entirely! So this issue should not be ignored or overlooked!

FWIW, I'm a huge fan of the idea of linear tracking. I think there is a way to make it work too; it will have to be a solution that has the vertical and lateral tracking masses being the same, while at the same time having the arm bearings in the same plane as the LP (to avoid change in tracking pressure on bass notes or warp).

Some of the alternative solutions like the Schroeder arm might do the trick. I'm still looking for the bearings to be in the same plane as the LP; not seen that yet.