I would have preferred the same cars as the other lines so as to keep the consistency as well.
IMO, most of the green line will be similar to the other lines and be grade separated so low floor LRV's aren't necessarily needed. Low floor cars might possibly be better along Centre Street up until 78th... I dunno.
I've used low floor trains before and while it makes for an easy build for a stop, it also has a few quirks. The cars themselves are a bit awkward when getting on with a stroller, or suitcase, as the low floor isn't level to the outside like it is with a high floor train/station. In cases like Melbourne it was level in some areas where stations were built having an 8" height adjustment similar to a curb, but un-level in other areas where they didn't do it. If you're going to go through the trouble of making an 8" high platform, you're halfway to building a Sunnyside type station.
Also the cars I was in, had two different levels of floor inside the car itself, which made it again awkward for people with strollers, suitcases or even bikes.
If it was for a 'streetcar' line I would be all for the low floor vehicle, but as a mostly grade separated line, I'm not so sure.