If you want to build up your skill and understanding of sourdough, Bread Matters could not be a better role model, but if you have already developed your own sourdough technique, or alternatively if you want to make the odd stunning loaf without the 24:7 commitment The Handmade Loaf offers a cornucopia of possibilities.
One problem is that if you try to follow more than one sourdough author at a time you can end up confused. Is 'wetter better' or is drier higher? Both BM and HL are excellent but I suggest that if you are starting on your sourdough adventures you choose one and adopt that style before adapting it to your own experience. If you've already got your own style you can adapt from both.
These two are two of the best guides available to the sourdough adventurer.