I'm coming from having a few Android devices over the past couple of years, last iPhone I had was the 4. So nothing on the iOS platform to fairly compare it to at the moment; but in comparison to my HTC One M7 I had for the past year, I do find my iPhone 6 to be reporting a lower signal strength.
I live in a 14th-floor apartment, and my signal fluctuates between 4 and 5 bars; at my work it's anywhere from 2-4 bars, but often closer to 2 where I spend most of my time. The HTC would almost always have 5 bars at home, and usually 3-4 bars at work.
This may just be a difference in how the iPhone calculates signal strength however. Hard to judge since each of these devices may use different radios, calculations etc.
As of yet I've not had any dropped calls (I rarely actually talk anyway, lol!), but I have had my data cut out on me in my underground parking, which rarely if ever happened with my HTC.
*** Side note: If the iPhone can't obtain an LTE signal, will it always show/fallback to 3G, or would it also show 4G? My HTC would fallback to 4G, and I don't recall it ever showing 3G or anything else below 4G speeds. ***