This depends on a lot of things, but usually Tilix.
I used GNOME Terminal for a long time. If I needed multiple terminals side by side, I opened two windows, or used tmux (I use tmux a lot, especially when developing directly on a server).
A few month ago I switched to Tilix locally. It fits perfectly with the GNOME environment, and it does everything I usually use termux for (but not everything, so tmux will remain).
Finally, I sometimes use the plain old text console (even though it's on framebuffer, so instead of 80x25 I get a much bigger screen). Since I began working with Unices in the 90s, graphical environments weren't as widespread as now. I got used to it so much I switch to tty2 every now and then.