Recs.
Updated
rxvt-unicode is a fork of the well known terminal emulator rxvt.
Specs
Pros
Pro Fast text rendering
Rxvt-unicode has very fast text rendering, being able to render hundreds of MB of text in a very short time.
Cons
Con Unicode characters that are too wide are blanked instead of clipped
If a character in a backup font is wider than the base font, urxvt substitutes the non-displayable character. A large letter space will show the wide characters, but the result is not reasonably spaced. There is a patch from 2014 that the urxvt maintainer will not merge.
Con Requires work to configure useful functionality (clickable URL's, font scaling, tabs)
Con Unicode rendering is buggy
There are a few references to urxvt's buggy rendering, such as unicode combining characters, which bled through during scrolling.
Con No support yet for 24-bit "True Color"
Though this is still not available, you can download the patched version for 24bit, here.
Con Font size cannot be changed on the fly with the mousewheel
Sometimes you may need to enlarge the font to improve readability, or shrink it to have more real estate and "hawk's eye" view of data. In rxvt you need to change the configuration file or use these commands:
$ function fontsize
{printf '\33]50;%s%d\007' "xft:Dejavu Sans Mono:size=$1::antialias=false"}
$ fontsize 22
Con No option to have a "reverse color" cursor
While you can choose the color of the cursor and the character under the cursor, there's no automatic "reverse color" for the cursor. This makes it impossible to use rxvt-unicode if you have a light background terminal and a dark background editor.