I have used most of the people listed above and would say that smarthawks opinion is to be valued on this subject.
I had an "Eisenburg" engine in the shop a few weeks back and it seems to be a nice job, Mr Eisenburg has a good reputation within the business but I can't comment further due to lack of personal experiance with his products.
N-M are my prefered option at the moment with all the jobs they have done for me being of a very high quality, a reasonable price and quickly turned around.