I'm more of a xHarbour fan, because of it beeing open source, very good supported (newsgroups on xharbour.com server) and very compatible with Clipper.
It is also available on several platforms, and compatible with several C compilers (xHarbour is sort of a 'Clipper to C' converter, but in a Clipper-like PCode way), and has full OO extensions, and possibility to insert native C/C++ code.
There are several free and commercial graphical extension libraries (GT drivers) to allow Windows or Linux 'native' apps.
AFAICS, xBase++ requires quite severe code-adaptions to get it gooing, but I never really tried (only occasional tests).
Best part to me is, I can produce 32-bit and 64-bit ready executables royalty-free & cost-free ;-)
HTH
TonHu