I haven't, unfortunately, compared to the other units, but I have owned the Aqvox for well over a year now and am extremely pleased with it.
The Aqvox is unique, I believe, among those you mentioned in that it has both balanced inputs and outputs (the others have only balanced outputs). If you heard it at the dealer without the tonearm leads being modified for truly balanced connection then you only heard about 80% of what it's capable of. The balanced input is much more critcal than the balanced output in terms of getting the most from the Aqvox.
If you were going to go MM (at least long term), I probably wouldn't do the Aqvox. For MC's (either high or low output) going balanced from the cartridge, it is literally plug and play with the current injection mode (I believe the only phono stage in the world offering both fully balanced inputs/outputs and current injection mode); you will never have to even worry about loading.
To say I've been happy with mine is an understatement.
