The first thing you should consider is price.
If you're in the market for a more expensive machine (1000+) it may in your best interest to look around at local dealers. Since you're spending a great deal on your espresso maker, it would be ideal to live in close proximity to where you are purchasing it in case anything goes wrong. Plus it is often easier to talk to someone face to face when you are comparing the more advanced characteristics of the expensive machines.
If however you are looking to buy an espresso maker in the $100 - $500 price range, you will find that online is where to buy espresso machines to get the best deal.
The reason for this is because there is a much larger market for espresso makers in this price range. There are more people looking to buy cheap to moderate espresso makers than there are for the more expensive models. As a result, there are more products available in this price range.
Since online sellers have access to a much larger market (global) they are able to lower the price per machine. You can take advantage of this by purchasing your new espresso machine from a big seller online.
But after determining to buy an espresso maker online, many people are still unsure of where to buy espresso machines from amongst all the different sellers.
In my opinion, one of the best sellers online is Amazon.com. They are one of the more reputable ones out there and they frequently have the lowest prices on most of their products. It is worth it to check out some of Amazon's prices before you commit to buying a new machine, because chances are, Amazon has the most competitive price for the machine your interested in.
If you're looking to get the best deal on a new home espresso maker, online is often the best place to find out where to buy espresso machines for the most competitive price. Of course, the only thing you need to worry about if you buy it online is shipping - but if you buy it from Amazon, than shipping is FREE.