I have both tunze and vortech powerheads...
anyone who tells you vortechs are silent is painting a rosy picture.. they are NOT.. I've got them on a fish only tank and anything over about 50% strength is easy to hear from across the room.. if they're on lagoon or wave making mode.. you can especially hear the unit ramp up, then slow down.. the pattern is unmistakable..
the tunze 6055s that I run, however ARE.... I have them set up to oscillate (alternately) and they create a mini wave in my tank by their selves.. they are silent, and I don't mean really quiet but if you're listening to them, you can hear them.. I mean the only way you can even tell they're on is to stick your ear on the outside magnet.. then you can hear them ramp up/ramp down...
I think that Vortechs are hot right now, because they are new.... so I think a lot of people are drinking the Koolaid where Vortech's are concerned.. but they are GOOD powerheads.. and they have great control features..
but having both... I prefer the Tunze (matter of fact, I just bought a nano wavebox to add to my Reef system.. can't wait till it arrives)