Your choice MSX or C64

Isn't Great Giana Sisters fairly compelling proof that Super Mario would also work on a C64?

Otherwise, it's too hard a question. The C64 is exactly one thing, the MSX is an array of things, from the lowliest 16kb MSX1 up to the you'll-never-see-one Turbo R. Though maybe if somebody went back in time and turned you into a C64 person from birth you'd have had a chance to enjoy the DTV and now the Mini.

To me the minimum MSX(1) is one with 64kb of memory. Models with less existed, but were (are?) rare and unpopular.

MSX1 was also vastly more common (at least back in the day) than any other iteration of the series, so in this sense I guess it makes sense to compare C64 to it. But that doesn't mean that MSX2(+) or TurboR could not be important to some - and are still official MSXes! The question becomes much more difficult to answer if you consider them (maybe you should have limited the question to MSX1 only? You have still limited it to C64, and chose not to include C128 or even Commodore Amiga)

I prefer the MSX - and the reason I do, is that it was the system I was more familiar with in childhood (C64 was very familiar, too, though). In a single word: Nostalgia.

If I try to think objectively outside that rationale - I think I'd still prefer MSX. Somehow it is more easy to hack (both S/W and H/W), but that might be just because I'm more familiar with it. Community and vast array of old and new software makes it also more compelling (though, I'm sure there is also loads of stuff - old and new - for C64 I'm not even aware of). OTOH it was designed to be more expandable (whereas C64 was not). I can see benefits of the C64, though (better sound and video capabilities OOTB - but that didn't always translate to better games).

Me like both.

Alas even the Commodore 128 has the weird two key cursors, I think. So you're stuck trying to hunt down a C65 prototype:

... which probably means spending at least a solid $20,000.

Or find a C64 DTV and solder on a PS/2 connector. Though I think its SID reimplementation doesn't have the filters. The C64 Mini has regular USB sockets but only as much of a C64 as is any other modern emulator.

Though I feel like both the SX64 and a two-box C128 exist with detachable keyboards? So you could wire up something better?

EDIT: or just buy and install one of these. Another C64 advantage is: there's so many of them around, all identical, that it doesn't feel so bad to mod one.

Last project i saw for C64 a time ago was "Caren and the Tangled Tentacles". Very impressive.. It looks so nice and so cool!

Youtube Link I like the part from 21:00 ... The nice shadows etc. Especially when you take the hardware in mind.