I would recommend a vertical TMR mixer for several reasons:

1) Simplicity.  No belts, no chains, no bearings.  You have a pto and a gearbox.

2)  Hay.  The verticals can handle hay much better than any auger or reel machine.  Even if you do not currently plan to put hay in the TMR, you might decide to in the future.  I do not currently use any hay in my mix, but I have had to add some in the past and will in the future.

3)  Resale.  TMR mixers seem to be the fastest depreciating equipment on a dairy farm.  But the vertical will hold its value better than an auger due to bigger demand.

4)  Life.  The verticals will last longer.  There are not as many wear items and the parts that do wear seem to be built a lot heavier. 

The verticals will mix just as well as the horizontals.  The equipment dealers in my area are happy to let you demo any piece that you want and I would highly recommend that you ask your dealer(s) to do the same.  Try a couple different mixers to see what will work for you.