xterm brags that they have the most faithful emulation of the DEC vt100/220/320/420/520 state machines of any implementation on the market.
In summary, none of the other terminal emulators emulates "most" of xterm. Instead, they implement the most commonly-used control sequences, and there are differences between them.
I have Cygwin on my office Windows PC, and when I have to work with a VAX or otherwise use a complete and faithful terminal emulation, I use xterm.
If xterm had tabs, I would never use anything else. Since it doesn't, I use gnome-terminal under Cygwin. The xterm maintainer has interesting things to say about gnome-terminal:
A more recent GNOME Terminal uses the VTE widget. I observed version 126.96.36.199 in late 2001, which mentioned it in the credits (although VTE 0.1's ChangeLog mentions no date before February 2002). It does not implement a complete vt102: it was missing several features which can be demonstrated in vttest)...
...so I use gnome-terminal under Windows for most everything, except when I need extremely high-fidelity.
p.s. I will say that our production floor relies on the Reflections commercial telnet client. They like the old version so much that I had to wrap it in stunnel - there were too many objections to the new(er) ssh versions. I really don't like Reflections myself.