Having done some research on terminal emulators today, I feel the need to hail the virtues of
xterm. This FAQ documents a lot of the bugs in other terminal emulators which aim to be
xterm or VT-100 compatible. You can also use
vttest to reveal a lot these issues for yourself. What puts a lot of people off of
xterm though is the lack of a menu configuration. This leads a lot of people to think
xterm is not configurable at all, however it is in fact highly configurable, it just has to be done via files like
.Xresources or command line options.
More gripes include lack of clipboard support and so lack of copy/paste with
Ctrl-Shift-V by default, however this can be overcome. Another is the lack of tabs, however many advanced Linux users prefer to use
tmux or GNU
screen which provide equivalent features.
This leads me to the real answer to your question -
screen can be used to connect to serial port and should work on Cygwin despite
/dev/ttySX not showing up with
ls. With this you should be able to use any terminal emulator you like, be it
xterm lacks many modern features and so may not be for everyone, but it is work noting that it is difficult to match what happens under the hood.
In case the link dies, here is the syntax for using screen as a serial terminal:
screen /dev/ttySX baud_rate,cs8|cs7,ixon|-ixon,ixoff|-ixoff,istrip|-istrip