I much prefer the UE900 over the TF10. The TF10 sounds very disharmonic to my ears. Even though its bass performance is incredible I prefer most dynamics over the Triple Fi. I also didn't like the Shure SE535 so I picked the W4 at the time. Some things did bother me and it is too mellow for my taste. The UE900 improves in that aspect.
The UE900 has a very light veil over vocals, yes, but it's far less prominent than with the W4. Soundstage of the UE is smaller, but also more intimate whereas the Westone has a much further distance and mostly expanding left and right.
One big problem with the W4 is that the bass loses all of its punch at lower volumes. It just disappears. Bass quantity scales with volume which bothers me a lot - yet you cannot get rid of the mid/upper bass and lower mids hump without proper EQ. With the Logitech I can listen at very low volumes and still have dirty bass punch on Hip-Hop tracks.
If you don't mind the points above, I think the W4 is the slightly better IEM. Personally, I prefer the UE900.
Build quality and comfort is amazing with both. I prefer the aggressive blue looks of the Logitech as it's a kinda offensive punch towards Monster Beats. :D
On other days I might prefer the humble black plastic and skinny cable of the Westone 4.
The UE900 are starting to get more and more apealing, as I keep reading very good reviews and impressions about them... Ultrazino, from the location in your profile, you live in Germany, right? Can you tell me where did you get your UE900, please? PM me if you like...