The short answer is that people will disagree on what the best machine is. I, personally, love the current La Marzocco machines (the FB80, GB5 and Mistral). I have also worked on the Synesso Cyncra and Id rate it not that far behind. I have heard that a Wega Sphera has the same guts as a San Marino Lisa - if this is true, I would expect it to be a shocking choice.
The longer answer is that we would need to know what features you are after so that we can sensibly recommend a machine that will match your expectations. For example, are looks important? Are you after a machine that is easy to use? Or one that will maximise the quality of the espresso that you are serving? Do you need to be able to churn out buckets of milk, or just cups? Do you need to be able to run on a low amperage? Are your staff well trained? It may be that you will have to compromise some things to get others.
The complete answer is that the machine is only a part of a the bigger picture in serving excellent coffee. If that is your true goal, you will also need to take into account things like the coffee that you are using, how well trained your staff are and the grinder that you are using. If I were to walk into your restaurant, I would order coffee if I saw that the brand that you were using wasnt terrible and your staff looked like they knew what they are doing (eg. empty dosing chamber in the grinder). I would not order coffee if you had one of the machines that I mentioned above, but it was teamed up with a brand of coffee that I know is usually stale and if your staff didnt look like they know what they are doing.
(Oh, and seeing as I mentioned grinders, Ill say that I think that the big commercial conical grinders like the mazzer robur and the compak k10 wbc really do make a difference compared with the flat burr grinders that you usually see.)
Frankly, I think that most restaurants really let themselves down on the coffee front. I love my food and I love my coffee, but I despair that I can only think of one or two restaurants that I would go to for an extravagant meal followed by a coffee.
I wish you the best of luck, and I hope that you end up serving great coffee!