I see the question come up in user forums. People are not sure what the difference is between the Amazon Echo, Dot or Tap and therefore, which one to get. Simple answer.It all depends on what you want. They are all great devices. Let's take a look at which one might be best for you.
Echo is Great
If you don't have a bluetooth speaker then the standard Echo is the way to go. There is a reason Amazon has sold an estimated 5 million of these things. It is well built, high quality, sounds great and looks good. Most people find the audio quality from sufficient to very good. There are numerous reviews of the Echo from big media outlets that will tell you what Echo is all about, how you can use it and what the technical details are.
Dot is Great
If you already have a good bluetooth speaker, the Dot might be better for you. You can save on the cost by using the Dot through the speaker you already have. At the current price, the Dot is an especially great value. You also might prefer the smaller size of this device. The built in speaker of the Dot is very low end and suitable for voice, but does fall a little short on sensitive ears.
If you are an audiophile you will probably find the speaker quality of the full size Echo on the mediocre side as well. Mostly because at the price point they are being sold at, they still have a hard time competing with audiophile quality speakers. As a result, if you consider yourself an audiophile (you know who you are), you'd probably be better off with the Dot because then you can send the output to your own speaker system. VoiceDesigned did an overview of the technical differences with Dot if you would like a deeper dive.
If you are looking at getting one of these devices for someone as a gift, you cannot go wrong with giving the Echo or the Dot. I would say most people like these two the best.
Tap is Great
The Tap is for two types of people. The first group is those who like portability and the ability to easily carry the device around. The Tap is battery powered, but has a charging station, making it perfect to grab and carry. The second type of person who will love the Tap are those who are concerned about privacy and have a feeling that Amazon and the CIA are listening in on your living rooms. The Tap has a button on it which is what you use to initiate voice commands. You do not use a wakeword and the unit is not 'always listening'. VoiceDesigned did a deeper dive into the differences on the Tap.
UPDATE 2/9/17: A new firmware update allows you to enable or disable the hands-free mode. By default you still use the button to give commands. However, with the new feature turned on (from the Alexa Companion App) you can now use it hands-free, just like it's siblings.
I hope this helped make up your mind. Most people find they end up with more than one device. The Echo is great in the kitchen as well as the living room. However, once you find yourself working with home automation and music and all the other great things these devices can do, they end up with additional Dot devices, sometimes one in each room.
So, which one you you going to start with?