I dont know much about them but I would love to have one!
The Kenwood Chef is the top of the Kenwood range as I know it. It probably has a bigger motor and certainly has a bigger bowl than the Junior. It also is stainless and metal as opposed to plastic.
Then there are the other machines that are in the same range, like the KitchenAid. They are also very good build quality and worth a look, similar looks too. Though I think that the Kenwood has the kudos as it really has been around forever.
Funny enough, Sunbeam does a similar machine in their so called Cafe Series but I wouldnt touch one with a fifty foot barge pole. Sunbeam had this style of machine for years too. Id only stay away from them because of the current coffee machine that seems to have endless problems.