Lumia Icon. I have one right now (white one) and it's the best Windows Phone overall. I had the 1520 before on AT&T and it's size was slightly annoying, if nice for stuff where screen "real estate" is important). Only drawback is the lack of microSD, but for my own purposes 32GB is fine. I think the speakers on the Icon are not quite as loud as the 1520's, but I no longer have the 1520 (cracked the screen when I accidentally dropped it ) to do a side-by-side comparison. The Icon is acceptably loud, though, I've just been spoiled by the 1520 and HTC One (M7 and M8).
The One (M8) is also a strong contender. I had the Android version of it and loved it for the body, speakers, and display. The Icon is no slouch, though, it has a gorgeous AMOLED display and the body is excellent. I don't no why some reviewers have said the Icon's design is plain - I'd say it's elegant; I much prefer the matte back and very subtle curve to the glossy 1520, which was slippery. The flat aluminum sides make it look a bit boxy and iPhone-like, but I don't think that's a negative.
I agree with Imaginer about the SoC. Everything so far is fast enough and smooth. Haven't got around to putting 8.1 update on it yet, though. I also haven't had the Icon long enough to test the camera, but so far it seems to be on par with the 1520, which is better than the One. The One isn't bad, but it and it's predecessor always seemed to only do better in low light and macro shots than its Android brethren - for everything else it was acceptable, but not as good as the other flagship phones. The Icon, on the other hand, is worth getting for the camera if image quality matters. Only the 1020 and the iPhone 5S are better with any consistency.
I *may* end up selling this phone when a new PureView successor to the 1020 comes out if it has an appreciably better camera, but for now I really love this phone.