I've used both, different models and generations. I would take Tunze hands down.
For me:
Tunze 6105s- Dead silent, I cannot hear them with my ear an inch from the tank. They are adjustable and easily hidden in the corners of my tank, with a max of 3" of cord in the tank. They are a highly reliable pump, with a long proven track record. I added the 6205 impeller housings, and the flow very similar to the Vortech.
Vortechs- I found them noisy, all 3 I tried. With them on 100% or pulse, the noise could be heard 2 rooms away without trying. To use them optimally, you are pretty much stuck with them being mounted to the sides of the tank, which was an eyesore on my 3 viewing panes. The cord, although not in the water, still is very visible on the outside. They are more prone to problems simply beacause of the technology, althought the support is great.