Exchange 5.5 upgrade or new install?

We have recently upgraded our DCs to Win2K w/ active directory, and we are now ready to upgrade our Exchange 5.5 running on NT4 server to Exchange 2000 on Windows 2K server. We have had not encountered any issues with our Exchange 5.5 server, which is handling approx. 125 users. Would you recommend upgrading the existing server to Windows 2000 server, and then installing W2K exchange (which would be the easiest to implement) or to start fresh with a new W2K install w/ exchange 2K and then migrate user mailboxes over?

What are your experiences with the exchange migration upgrade or new install?

Thanks,
Dan