Dell make competively priced systems and can be reliable. Their call centre is in India and it can be a bit difficult for them to understand you if you have a dialect and vice versa. I understand that they tend to have components that are unique to Dell.
Evesham are UK based and in my experience are easy to speak to when placing an order (no experience of after sales). They tend to be a little more expensive then Dell.
I've bought from Dell and Evesham. 6 from Dell, 2 from Evesham. I have had one problem and that was with a Dell which was dead on arrival and there was a mix up with the order in that the spec ended up being incorrect (language problems?). Refund happened ok but not without small hassle over collection. Others have had no problems. Very pleased with the remainder of the Dells and the Eveshams have worked fine and like them.
Bottom line - not much to choose between them.