The easiest to set up for production will probably be Apache and mod_rails (passenger). If you want to be using the new hotness, you could give nginx and passenger a whirl.
For development mongrel is usually the easiest to work with. Most Windows IDE's (RadRails, Netbeans) give you the choice to use Webrick or Mongrel for development work and let you control the servers from the IDE itself.
Update
Four Choices
There are really four choices, well, plus WEBrick, but that would be an unusual choice for a production server. Approximately in order of increasing complexity...
nginx + Mongrel
nginx + Passenger
Apache + Mongrel
Apache + Passenger
(There is Phusion Passenger Standalone, but that's really an nginx + passenger compiled together, so I'm not counting it, although it may be a good option for some people.)
A larger site may then add specialized layer 7 hardware (NetScaler, F5, ...) in front of the servers.