I don't use Entrourage (mostly cuz I don't trust M$ but that's a different story), but from all other mail programs I've used - I love Jaguar's version of Mail the most!
If you have multiple accounts set up, you can view mail from ALL of them from a top-most (parent?) folder while keeping each account's mail seperated.
The Spam Filter really is pretty good I'd say. At first it lets certain spam through but just click on the "spam" or "not spam" button and it corrects itself for future mail/spam. I had it in Training mode for the first week and it has cought all Spam coming in since (without affecting real mail)!
Funny thing is - it even cought spamthat came through a webform you have to fill out (a spammer REALLY went out of their way to send spam to one of my accounts) but yet all other mail that comes in through that webform is not affected!
The fact that it works with OSX's Addressbook is a major plus for me, and the coming of iSync and iCal will make it that much more valuable to me.
Only irk that gets me is that it does not always download the entire email to the hard drive, and since my Internet connection from home is not at all reliable it can sometimes cause problems reading my... but it's a lot better than it was before Jaguar.
If anything, try both Mail and Entourage at the same time, have one leave mail on your server (or use IMAP if possible) and see which one works better for you.