Honestly those 3 options seem to be much of a muchness, all of them have their fans and none seem to have any serious issues. As you say there may be an advantage in buying from the people you are already dealing with.
On CS the K3 gets the most noise, but as its a commercial site and many of the sponsors have had special deals on the K3s that may be a little unrepresentative. (Checking on Home-Barista they do seem to get a good report card.)
Other options are the small Mazzers and Macaps, although you would probably have to look second hand at that price point.
If you use the email@example.com email it will go to all sponsors and you could ask them what deals they have on at the moment - i suspect end of financial year is a good time to be purchasing.