I agree with plain xterm. Others tend to annoy me.
It's true there are a number of oddities about xterm that might put off people who've never used it before. By default no scrollbar, and once you enable it, it is kind of odd in that you don't use "modern" conventions to interact with it. Its menus and other features are hidden by keystroke combinations that are probably hard to discover if you don't already know about them. I don't like some aspects of the default configuration. I've heard the code is a mess internally, although I haven't checked. Etc.
But I still think xterm is the best. Some emulators flicker when scrolling; not xterm. It just seems faster, and I'm spoiled: even a small fraction of a second response time seems excessive to me. Uses very little RAM. Very configurable if you actually take the time to search through the man page. No superfluous decorations around the terminal (even a scrollbar) unless you want them. Doesn't depend on any huge modern GUI toolkits; if you can run X at all, then you can run xterm. It's available everywhere; get used to it once, and you aren't constantly getting used to other terminal idiosyncracies. Etc.
My personal configuration:
! Very useful to quit out of vi or less, and still refer to
! what you were seeing while typing next command:
! works better with the black background I like above: