Honestly, Konsole is fantastic. On Gnome I use Blackbox, on Sway I use Foot, but if you’re on KDE you don’t really get better than Konsole.
Alacritty and Kitty are both terminals I used to use back when I was on i3wm, they’re perfectly usable, but I don’t think the average user will gain any tangible benefit from replacing Konsole.
Arc for sure! It’s chromium based, unfortunately, but has unparalleled tab and workspace management, and is unfairly sleek and nice looking!
Other than that, Firefox is always nice, and Orion is interesting as well.