Das 135mm f/1,8 hat zum Glück kein ausfahrbares Frontelement.
Beide aber haben einen Internen Fokus.
Das Zeiss 135mm f/1,8 ist das lichtstärkste Objektiv seiner Klasse. Die Konkurrenz hat nur f/2.
Wenn 85mm zu kurz sind, würde ich auf jeden Fall das Zeiss 135mm eher nehmen, denn in Richtung Tele
kann man nie genug bekommen.
Und an der Alpha 900 ist das Zeiss 135mm fast wie ein 85mm an einer APS-C Kamera a la Alpha 700.
Also da Vorsicht. An APS-C hätte man das Zeiss 135mm sicherlich weniger für Portraits bei kurzen Abstand gebrauchen können,
an KB bzw. FF sieht die Welt aber wieder anders aus.
The Zeiss ZA Sonnar T* 135mm f/1.8 is an exceptional lens - technically it's even slightly superior to the already great ZA Planar T* 85mm f/1.4. The resolution as well as the level of contrast is nothing short of outstanding and that's straight from f/1.8. The quality of the bokeh (out-of-focus blur) is next to perfect for a conventional lens. Unfortunately longitudinal CAs, sometimes also called "Bokeh CAs", can be relatively pronounced at large aperture settings - a typical problem in this lens league but a bit unfortunate nonetheless. Distortions, vignetting and lateral CAs are non-issues in field conditions. Thanks to an all-metal body the lens feels very solid. If you're nit-picky you may criticize the lack of sealing and a little play in the focus ring when changing the focus direction. The AF speed is still fine despite the rather dated screw-driven AF approach. The entry hurdle for the Zeiss ZA T* 135mm f/1.8 is quite high at around 1300EUR/US$ but if you want the very best this is the one. Highly recommended!
Quelle:
http://www.photozone.de/sony-alpha-aps-c-lens-tests/381-zeiss_za_135_18?start=2
The Zeiss ZA Planar T* 85mm f/1.4 is a great lens but we expected no less than that anyway, didn't we ?

It is already able to produce exceptionally sharp and contrasty results straight from f/1.4. The excellent performance peak is reached around f/4. The center to border quality is very even (although that's a lesser issue regarding the typical applications of such a lens). The quality of the bokeh (out-of-focus blur) is buttery and about as good as it gets. Distortions, vignetting and lateral CAs are non-issues in field conditions. Nonetheless there's also bug - longitudinal CAs, sometimes also called "Bokeh CAs", are very pronounced at large aperture settings but that's a fate the Zeiss shares with fellow lenses such as the Canon EF 85mm f/1.2 USM L and Nikkor AF 85mm f/1.4D. Thanks to an all-metal body the lens feels very solid. If you're nit-picky you may criticize the focus ring which shows a little play when changing the focus direction. The AF speed is fine although nothing to rave about. At around 1200EUR/US$ the Zeiss ZA 85mm f/1.4 isn't cheap but definitely worth a deep thought regarding its optical qualities.
Quelle:
http://ww.photozone.de/sony-alpha-aps-c-lens-tests/374-zeiss_za_85_14?start=2
Technisch gesehen wäre das Zeiss 135mm f/1,8 womöglich die bessere Wahl.
Auf jeden Fall hat man mit den Zeiss 135mm f/1,8 das Gefühl von schweres Glas, es ist wirklich ein Brocken.

Ansonsten eine schwierige Entscheidung, wenn es um die Anwendungsgebiete geht.
Beide ernten nämlich eine sehr gute Bewertung bei den Usern:
http://www.sonyuserforum.de/reviews/showproduct.php?product=145&cat=5
http://www.sonyuserforum.de/reviews/showproduct.php?product=144&cat=5
http://www.dyxum.com/reviews/lenses/reviews.asp?IDLens=300
http://www.dyxum.com/reviews/lenses/reviews.asp?IDLens=317