I have iPhone 6 with iOS 8.1. I commute every day for 40min from home to work and back, and there are two places in the route that I know have very low signal coverage and are a very good test for mobile phones antennas reception.
With my previous iPhone 5s, in these two places during a call it happened to lose some voice samples, but the call was never dropped.
With the iPhone 6 the calls are always dropped in both places.
I don't look at signal bars because they are only a signal indicator, but the dropped calls are a clear fact that the iPhone 6 reception is worse.
Also the iPhone 4s was worse than the 5s but better than 6 because it lost many samples, the voice became metallic, but very seldom did the calls drop completely.
Unfortunately with the 6 dropped calls are a certainty.