Vsonic VSD3S vs ZA Tenores short short version:
Let me first say that I find the Tenores to be a great IEM . I guess one could say that they're a pretty straight upgrade from the Sony MH1C with much better controlled bass and the same extremely smooth over all presentation.
My main grip with the Tenores, compared to the VSD3S, are that they're a bit to thin sounding for my liking and I also find them to be to smoth (especially in the highs). The sound of the VSD3S are much fuller and it lso have a bit more bite in the treble making it more suitable for my liking. I actually can't think of one area were I think the Tenores perform better than the VSD3S. That's not saying that the Vsonics are better at everyting but they're better for my taste in the two things metonioned. Both sets offers very good separation and soundstage.
Please also note that I don't really like the Sony MH1C that much due to it's boomy bass and to smooth treble so users happy with the MH1C (and there's enough of them) should probably be very happy with the Tenores as well.
There also seem to be a fact that there's quiet some variations between different pair of Tenores, driver flex problems and more than one report of faulty units as well. This gives a feeling that QC is poor or even lacking and seem to make them quiet a gamble to purchase. That being said my pair works as intended so far.
Vsonic VSD3S vs Astrotec AX-35 short short version:
I find the AX-35 to have too recessed mids and boomy mid bass in it's stock configuration. I've modded my AX-35 by taping off all the vents, adding a 50 OHM resistor and using them with Sony hybrid tips. In this configurtion they're more balanced with the mid bass being tamed and pushing the mids a bit more forward.
I find the modded AX-35 to be really nice and enjoy them as much as the Tenores. They're way different though. Compared to the VSD3S the AX-35 still have a bit too recessed mids for my liking. I feel like they're a bit schizofrednig with some darkness in the lower mids combined with some brightness in the treble. The AX-35 is every way as full sounding as the VSD3S but the Vsonic has better extension in both ends and sounds much more airy as well.
Due to the slightly recessed mids on the AX-35 I always keep pushing up the volume on them wich aslo brings out more mid bass than I would have preferred. The VSD3S on the other hand sounds great even on low volume. Just like with the Tenores compared to the VSD3S i don't feel that the AX-35 performs better than the VSD3S in any area wile the Vsonics performs better in some. Both set offer very good soundstage and separation.
The build on the AX-35 are excellent and they should be able to survive for a long time.
Hope this helps