Both Tomo and Varian(trilogy w/rapidarc) are very highly rated.

My cancer treatment center considered Tomo the Gold Standard for head and neck where numerous areas needed irradiate and avoidance of critical structures was paramount as was necessary in my case.

I am not sure if Varian has a newer model out now or not, but
The multi-leaf collimator leaves on the Tomo were thicker and I believe faster so there should be less scatter radiation.

A nice thing about the Varian is that the daily CT scan only uses about half the X-ray dose of the Tomo, and of course how fast it is.

I understand the next generation of Tomo will be much faster and adds another dimension of beam control which my RO contents will actually increase its current advantage over volumetric arc therapy systems like Rapidarc for complex cases .

I remember reading an article that arc therapy really can't effective use all its 360 degrees where Tomo apparently can.

My ENT contents his OC patients that get Tomo seem to recover quicker and perhaps more fully from dry mouth. The cancer center has several metro locations and only one Tomo unit so most of OC patients get treated on a Varian system and two of them in my support group seem to have considerably worse dry mouth than I do (mine is negligible).

When there is a choice, I would consider Tomo for OC, and leave the RapidArc for less complex targeting, but it is good that you have such fine contenders to choose between.