Kevin,
Slightly confused. I don't know of any 'Evolution Mail Servers'. Are you talking about using Evolution as your mail client (instead of the built in OSX Mail)? I am going to guess that this is so you can access more features (calender?). Which mail server are you currently using? I assume Exchange? For the Macs here, depending on the user, we mainly use Thunderbird with the Sunbird/Lightning plugin for calendering. I would have to say that Entourage / Evolution seems to be the "easiest" to get set up with Exchange, but easy just means a hot poker in one eye not both. With the recent Novel /MS announcement, Evolution may just get even easier to use. I am keeping my eye Novel right now. All in all, It's just a question of what are you wanting to do/ what features are you looking for?
-Joe