VPI Aries vs. VPI TNT III

MY TNT 3.5 (SME V arm) has never gone out of adjustment once I have set it. I have checked it at several month intervals over four years of use. Not once did I need to re-level the TNT or readjust the SME. Weird that my experience is so different from others in this regard.
The only part that I have had to be somewhat careful about is the tri-pulley unit sometimes moves if I have changed tone-arm cable or something. I have caused the pulley unit to shift (or the base to shift) in these cases; so, I don't consider this a TNT problem at all. Besides, a slight nudge of the pulley unit probably does nothing to hinder performance--unless the pulley shafts touch the TNT base, of course.
I find the TNT reassuringly stable and simple to use.

I have a TNT version 2.5 (close to III) and it's been nothing but steady over the short while that I've had it. Once it was set up, it remained set up. Currently using the 10.5 arm and an AT-OC9 (anyone have a good cartridge recommendation). I would highly suggest that you consider getting either a Seismic Sink or a Bright Star Rock/Air Mass assembly if you're going the Aries route. It has no suspension and the isolation devices would be a serious asset.
I am also the owner of 2 Well Tempered tables, an HW19 MkIV and an HW19 MkIII. All of these were serious upgrades from my Linn LP12 (talk about set-up problems!).

I know someone who had his TNT 3 upgraded to a TNT 5. He never mentions any adjustment problems. I will ask him specifically about the need to re-adjust next time I see him.

I had the Well Tempered (Classic) arm on a SOTA Sapphire a while back. A clever 'arm. The Morch UP4 is also a very, very good 'arm on the SOTA, BTW. In fact the Morch UP4 (with silver internal wiring) seems like a "sleeper" tone arm. For the money, it's hard to beat.