9", 10" or 12" tonearm?

Clearaudio has a line of linear tracking TAs that are typical CA quality (very high). Even the least expensive is expensive (to me). I'm saving for new TA and may spring for their lowest end model. 

Another problem with linear tracking TAs is their physical layout. Most will not fit under what I would consider a "normal" dustcover.

A long arm offers a lower degree of tangency error but has more resonances of the barrel ... this is the reason for sympathizers or detractors for the 12’’ arm

For example, I don’t love them but I appreciate the 10'’ arms!

It depends on the cartridge. Longer tonearms have higher effective masses. In order to make a longer tonearm as stiff as a shorter one you have to add more mass yet. If the cartridge has high compliance it will suffer in one of these arms. There are some examples of lighter 12 inch arms that are very stiff. The SME V 12 comes to mind.  Kuzma 4 Point arms are heavier but stiffer yet. There is no straight line tracker on the market today that I would prefer over one of these arms. I have watched Clearaudio arms tracking records closely. The cantilever always leads the arm like the tail wagging the dog. I am sure it is possible to make a straight line tracker work beautifully. I just do not believe it has been done right yet. When it happens I will be one of the first to jump on board assuming I can afford it. 

Sounds like new materials would be a benefit for the longer arm, lighter, stronger and low resonant......