The Portatube and vorz are two very different amps. Sound-wise, they can be compared. Both drive headphones and earphones nigh on perfectly with few to no artefacts. The Vorz sound is decidedly less shiny (a bad phrase for the sort of smooth/clean distortion you can sometimes get with valves). The Portatube has a lush high end that smacks a good one at every portable amp I've come across. It's a personal thing, though.
But, either amp perform very well. Technically, at optimal volume settings (matched to safe listening levels with same headphones on the out), the Vorz will technically outperform the Portatube. But, if you are a valve fan, that won't matter. I'm typically not a valve fan, however, the Portatube isn't a typical valve amp. It's not 'tubey', dark, or veiled. It's merely more intimate than a typical solid state amp, with the plus of a shiny high end.
But it's more than double the volume of the Vorz, runs hot, gets 8-10 hours of battery life.
I wouldn't consider one or the other if you value compactness. The Vorz is the only choice there. Absolute power, the Portatube will win of course.
If Vorzuge can fix the gain, either by incorporating the gain into the volume pot and lowering the aggression so that it can freely be rotated up to 50% for earphones and 100% for headphones, I'd not think twice. The Vorz is killer.
The VorzAMPs have excellent control of artefacts and resolution with low Ω earphones, but the gain is too high. However, VS the Continental V2 for use with low Ω earphones, there is no comparison: the VORZ has it beat in almost every regard: better resolution, fewer artefacts, lower noise, overall tighter grip. But, the Vorz lacks a gain control, which it desperately needs. Its internal gain is too high.