Today the default choice for a terminal program is Gnome Terminal
Recently over on the Fediverse, someone who's coming back to Linux asked what terminal program one should use these days. After thinking about it, I realized that my answer had to be Gnome Terminal (also), at least for the kind of person who's asking this question without any particular additional qualifiers.
I'm personally very attached to the venerable xterm, but xterm is an acquired taste with various issues in practice, so I can't recommend it to a new person. If you want xterm, you already know it (and you probably have several reasons why). Out of the various alternatives, I think Gnome Terminal is the default choice for two reasons.
First, Gnome Terminal is inoffensive and basically works. I believe that it has all of the features you'd expect from a modern terminal emulator, and if some aspect of its behavior or appearance isn't entirely to your liking, it supports a reasonable amount of customization. If I had to switch to Gnome Terminal for some reason I could probably get by reasonably well, even though various differences from xterm would irritate me for ages. Gnome Terminal is a perfectly reasonable and functional terminal program, which is the basic requirement.
Second, Gnome Terminal is pervasive; it's the default Gnome terminal program, and Gnome is more or less the default Linux desktop. Because of this, pretty much everyone is going to test things with it and make sure that they work okay, both in appearance and in performance. For example, a Linux distribution is certainly going to make sure that its choice of default monospace font works okay in Gnome Terminal; your mileage may vary in other terminal programs. Similarly, text colours vary between terminal programs but people are almost certainly going to make sure that their program's use of colours looks decent in Gnome Terminal. This means that you're less likely to run into irritations with Gnome Terminal. And if something does explode, if you're using Gnome Terminal in a standard environment (such as Gnome itself), then fixing it should be a high priority for your Linux distribution since a lot of people will be affected.
You can make a case for KDE's konsole on much the same reasons, but I think KDE and konsole are less widely used and so you're more likely to run into issues in distributions and with programs. You can get rid of the distribution issues by using a Linux distribution (not an alternate 'spin' of a distribution) that focuses on KDE, which will likely take care to make sure their choice of default fonts works well with konsole and so on. I'm not sure there are very many of these left, though.
(This elaborates on my Fediverse reply.)