A decent candidate for a BASIC dialect which includes 'the basics' (e.g. GOSUB for backwards compatibility with OLD programs) as well as a long-developed (since 2004) set of modern enhancements (objects, named functions, ...) : https://www.freebasic.net/
While I don't code in it for anything but fun and toying, it's what I learned on in the 1980s (Microsoft BASIC for the TRS-80 Color Computer 2). Also played a lot with Applesoft BASIC on the Apple IIe in high school.
Later I moved on to QBasic 1.1, QuickBasic 4.5 and PowerBasic 3.2.
My first software development job, about a year after high school, was using PICK BASIC (in the form of UniVERSE on the IBM RS6000 running AIX - my first exposure to UNIX).
Then on my Amiga with AmigaBASIC (IIRC?) then later AMOS...
I've toyed around with PBASIC (for the BASIC Stamp microcontroller).
(It's good that Microsoft still has a BASIC out there that you can point kids at. BASIC was Microsoft's first product and absolutely left a legacy across the decades.)
Also, I feel that as long as schools continue to require Texas Instruments graphing calculators for tests, that TI-BASIC will probably long have a place for teenage experiments when bored in classes.
Free, open-source, multi-platform.