Well you are going to get everyone to mention a different OS when you post a message like that.
What kind of games to you plan to run with your system? Every OS has pros and cons when it comes to gaming. The only big difference between 98se and ME is that most DOS based games will not run correctly if at all under ME. ME can also be a little buggy.
Windows 2000 is not really made for gaming but the OS will almost never crash. It is much, much more stable than ME. But users have complained that there is a drop in fps in their games and some games arn't supported.
On my system, I dual boot between Win2000 and ME. I do whatever I can on Windows 2000 since it is so stable and reliable and do all my gaming on ME. I personally have had no trouble at all running my games with Windows ME. There really isn't a "greatest, bestest OS" right now; however Microsoft claims Windows XP will be the "Greatest, Bestest" when that comes out later in the year. Since that basically joins Windows ME and 2000 into 1 OS.
My opinion is to go with ME or 98se and then you can upgrade to XP when that comes out and it SHOULD be a more stable OS. At least that is what Microsoft claims.
That is a great set-up by the way!