I much prefer all spindles. Spindles are classic, and they're a great place for greenery /lights at Christmas.

If you had all glass -- even if that were an option -- it'd look like "nothing", which seems a little uncomfortable /like you might fall. I also wouldn't like to keep that glass clean.

Splitting the two looks like you started changing the rails and quit (or ran out of money) halfway along the way.

I'd keep to one style. If you were going for a more modern horizontal style railing for the stairs the glass would work better, but the transitional look of the spindles and the ultra-modern glass are clashing a bit.

I had glass panels supported by larger “spindles” in my loft, looking down on the living room.

What about something a bit more contemporary such as shown below, combined with the glass?

1950's Split Level Contemporary Renovation · More Info

You are required to have a continual hand rail that goes the distance of the entire stair and wraps the corner between the upper flight and lower flight. There is no inexpensive way to do that with glass. It’ll be difficult enough to be code compliant with wood.

Additionally, split levels aren’t nearly a modern enough architectural home style to be putting in glass or cable anything. They are traditional style homes that should keep their traditional details. They look fractured and disjointed when you try to make them look like a downtown loft.

Either all glass or all spindle. I would not mix. This is another example if all glass.

I think all spindles and no glass would look the best.

Thanks everyone for your advice! I really appreciate you taking the time. Looking at the railings as two distinct styles (glass as contemporary and spindles as traditional) changes my perspective. I wasn't really looking at it that way. This design thing is really complicated :)

Spindles it is! Thanks everyone!