That all depends on your intended use!
Check reviews (and quick video below),but don't buy the original Show because the New Show will allow you to access YouTube videos via Silk. For me that is a huge improvement!
Generally, I would go for the new and improved models.
If you want a consultant to ask about the weather or what the difference between Feta and Goat cheeze is, the New dot sounds like the best option.
If music sound quality is important the Echo Plus has better SQ than the original Echo (which was good) and you can get a pair with their new sub for a 2.1 system.
However at that $ point I'd start to consider pairing a Dot with a pair of JBL LSR305's. The Echo sub may go a touch deeper than the JBLs, but I would not be too sure and the JBL's are a know "best in class" option for fidelity!
If you want to spend more for better SQ, I can give more options... just ask!
Depending on how much patience you can summon, I'd wait until Black Friday, as Amazon has historically sold the Echo gear at a pretty good discount (30-40% discount). A dot would be $30 instead of $50, however the introduction of the new models may affect discounts.