The real Dickie xterm: invisible-island.net/xterm/
I have to connect to a range of servers - Solaris old and new, SCO, Macs, Linux, BSD - and the real Dickie xterm gives me least problems and maximum compatibility.
Why the Dickie xterm? It's old-time standard compliant. Shift-leftclick or shift-rightclick on the Dickie xterm and you can control major facets of xterm behaviour that you will need when moving between many different Unix systems.
You can use the .Xdefaults configuration file to control your default settings (including handling those silly Solaris function key issues). You can control starting sizes and positions, colour, keystrokes, terminal settings, almost everything. You can even standardise the ancient Delete/Backspace incompatibility problem between Linux and Solaris and SCO and other systems. Copy that .Xdefaults file everywhere you go and your xterms function identically no matter what system or OS you are on.
If you find a copy of Alan Southerton book The Shell Hacker's Guide To X and Motif, despite the ancient title, you can configure your xterm to do amazing things and have wild menus and functionality and that can seriously enhance your productivity either as a programmer or a sysadmin.
The Dickie xterm is so standard that all old texts and books and hints work with it, yet it keeps up with modern practices. It just doesn't do fancy modern graphics like see-through backgrounds and other things that impede work but look pretty.