There is a linen closet in the hall outside the bathroom, but the talk cabinet is more convenient for towels. It is currently a guest bathroom, but also might be my mom’s bathroom in the future.

Your mother may find the tall cabinet much easier to use for towels than the lower cabs with doors. Besides, I always manage to clutter up open shelves. Drawers are always easier to use than lower cab doored cupboards. The second one would be my choice if there is a chance your mother will be coming to stay.

I like the second option as well. Visually, I think it looks balanced and well-planned. The additional drawers will probably be more useful than the lower cabinet with doors. And since you only have one sink, it makes sense to get rid of the other lower cabinet with doors...the first option almost looks like you intended to put in two sinks, but didn't. Another plus with the second option is that you have a well-defined rectangular backsplash area behind with sink (obvious edges, etc.).

Thank you @Carole & @Nancy in Mich - we were leaning toward #2 all along but then I got worried that it wouldn't feel open, like @palimpsest mentioned. I'm going to commit and be done with that decision. It will also balance the off-center window, and hopefully look more intentional.

To help it feel more open, you can do a counter-top storage cabinet instead of a tall linen cabinet. You make it 2/3 or 3/4 the depth of the counter. It still holds toiletries very well, and things don’t get lost in the depths. To protect the wood, you put another piece of counter material under the counter-top cabinet so that it is not sitting where water may splash up against it from the sink. It is elevated above the counter and looks nice, too. You can see several styles In THIS thread. I like the ones with little drawers for things like tweezers and nail clippers that tend to get lost in a drawer. You can often put an electrical outlet inside, so the tooth brush can be plugged in.