Dan Moren, writing for Six Colors:
The Dot is essentially a small version of the existing Echo, just 1.5 inches tall, as opposed to the Echo’s 9.9 inches. From what I can tell, it has all of the features of the Echo, as well as two new tricks up its sleeve: it includes a standard 3.5mm audio output jack, letting you connect it to an existing set of speakers; and it can connect to Bluetooth speakers as well, so you can pipe music from online music sources—Prime Music, Spotify, Pandora—to better speakers. […]
The Tap is, as rumored, a smaller portable version of the Echo—6.2 inches tall and 2.6 inches in diameter—complete with a rechargeable battery and charging cradle (you can also charge it via micro-USB).
I find the Dot to be the most compelling of the two devices. I like the idea of plugging it into a nice set of speakers for improved audio quality.