Get both focal lengths, but get the 85mm FIRST...it will be VASTLY more-useful. 135 is very,very narrow-angle in anything less than wide-open spaces. 135 is highly selective, and at less than 20 feet, is simply too narrow-angle to allow you to capture MANY typs of event scenes...135mm is a focal length I grew up with, and I own both 85 and 135mm lenses of various speeds, both f/2,f/1.8,and 1.4 models. For longer-distance candids, a 135mm lens is simply almost unbeatable--SHARP, wide-aperture, EASY to focus, narrow angle of view, shallow DOF at indoor ranges, and so on...BUT, at a wedding, there are quite often 5 to 20 people "in the way", and the long distances needed between the camera and the subjects means that 135 is just "too tight", or even worse, that people will come between you and the subjects because of the extreme distance between the subjects and you, that entire "zone" seems like "free space" to wedding guests who have zero idea that they are blocking your shot.
With an 85mm lens at 20 feet, the field of view is 8.5 feet tall, at that distance, so it can do a "tall, full-length" bridal couple's portrait, from 20 feet, no issues....with a 135...'issues' can creep up. From the BACK OF THE CHURCH, a 135 IS SWEET!
The 85mm lens is also VERY small and compact, and is exceptionally non-threatening, making it one of the absolute best candid lenses....people do NOT tense up or freak out when they see you with the Canon or Nikon 85/1.8 lenses...NOT the same reaction as when using a big, large, black lens like the 135/2-L...it makes you look like a "peeper"...the 85/1.8 is the exact opposite...I have seen the images from the Sigma 85/1.4...I honestly do NOT see why anybody would buy that lens instead of Canon's excellent 85/1.8 EF OR Nikon's truly SUPERB 85/1.8 AF-S G...no idea at all...