If you're using a full desktop environment like gnome or kde, using the builtin terminal might be a good starting point. That way you get consistent themeing out of the box and benefit from a consistent user experience. These terminals are pretty basic, but they get the job done. If you use the terminal often or even "live in the terminal", consider a more sophisticated product.
If you, for whatever reason, like suckless software and believe that patching source code is an acceptable way of configuring software, use st. The suckless terminal st, will take the least disk space and lacks basic functionality out of the box, making it very attractive to the average suckless enthusiast.
If you use wayland and want "speed" above all else, you can't beat foot. The foo terminal. Foot has the lowest latency of any terminal I've tested.
If neither of those two are appealing to you, but you own an nvidia or arm gpu, consider some old terminal. Test the gpu accelerated options and compare speeds with those old terminals. Depending on how bad the drivers are, urxvt might be a better choice than the following options.
This is often subject to controversial debates. Below I'll give you some benchmarks I use.
How fast the terminal feels is more important than these metrics anyway.
hyperfine for multi-run benchmarks.
time ( tree / )
time ( find / -type f -iname "*.md" 2> /dev/null; )
time ( ls )
time ( wezterm imgcat sample.jpg) or equivalent
GPU accelerated terminals have been hyped up for a while now. Alacritty has been hyped because of the rust hype but with it's two competitors I can't in good conscience recommend it. The speed debate between alacritty and kitty is childish at best. Pay as little attention to it as you can.
Kitty is a neat terminal with an image viewer and some other small utilities like a diff viewer. Kitty is pretty fast and has the highest graphical bandwidth/throughput I've tested. The kitty dev however is pretty delusional and rude, so don't choose this one if you're the kind of person that tries to contribute upstream.
My favorite terminal then is wezterm. Wezterm is incredibly feature rich, supporting 3 image protocols, asciinema recording and shipping with hundreds of themes. It's configured in lua, giving it some hypothetical programmability. Wezterm imgcat is about 10x faster than kitty icat, so if you regularly use the terminal as an image viewer, I recommend you use wezterm. Wezterm, once you disable the tab bar, isn't noticeably slower than kitty or alacritty in my testing.