Best email client to use with Exchange server?

I convinced my new employer to let me use a Mac for work, and they bought me a new MacBook. I had to assure the support staff that I would not be an extra burden on them since it is a PC/Outlook/Exchange shop.

I am connected to exchange server using IMAP, with IT support's help (so all the correct ports and protocols and security have been set). Still I am having serious problems:

1. Connection to exchange server is lost intermittently
2. Sent messages that do not appear in the sent folder
3. Discrepancies between folders in mail and folders on Exchange
4. Sometimes outgoing messages just hang and the status bar drops to '0 kb'
5. Attaching files can hang (especially .pdf's it seems)

Any thoughts? Could this be MobileMe getting in the way?

Should I give up on Mail and move to a different email client? Which one will work best with Exchange?