I generally use the shift key closest to the key I'm typing. For keys near the center, I favor the right shift key.
The keyboard would absolutely be the show stopper for me, if I didn't just get a new laptop last year. The lack of dedicated Page Up and Page Down keys is unacceptable.
I've used Chromebooks without them before, and I still to this day can never remember how to select while jumping to the end of the document, for example. It's like four keys all pressed at the same time in a very awkward way.
Down - Cursor trajectory
Fn - Page instead of Line
Command (Alt) - Document instead of Page
Shift - Text selection mode
(But I had to hit the keys and then look at my hands to figure out what they were, because I'm just used to keeping the modifier layers in muscle memory, so I could be wrong.)