A recurrent theme for many writers (of English), particularly non-native speakers and especially me, is whether to use ‘that’ or ‘which’. Here is Steven Pinker:
The real decision is not whether to use that or which but whether to use a restrictive or a nonrestrictive clause. If a phrase which expresses a comment about a noun can be omitted without substantially changing the meaning, and if it would be pronounced after a slight pause and with its own intonation contour, then be sure to set it off with commas (or dashes or parentheses): The Cambridge restaurant, which had failed to clean its grease trap, was infested with roaches. Having done so, you don’t have to worry about whether to use that or which, because if you’re tempted to use that it means either that you are more than two hundred years old or that your ear for the English language is so mistuned that the choice of that and which is the least of your worries. [Steven Pinker, The Sense of Style, Allen Lane, 2014.]
I am not two hundred years old, so that or which is the least of my worries; good to know!