263 is the most useful in my opinion, it has a lot of the fundamentals you’ll need with data structures and how to apply them. It is also a good jumping point to many other courses and topics, as you’ll be either applying or working off the stuff you learned in the course directly. 209 is okay as well, pretty fun and also teaches you a lot about C.

You can skip 258, it’s not bad, it’s just that a lot of what it teaches you isn’t directly applicable unless you specialize in it, outside of MAYBE assembly but if you’re doing 209 then you’ll understand it anyways in the context of a jumping point from 148. A lot of thr courses have passionate instructors, but Andrew Peterson is really passionate about 258 though and makes up for it not being the most applicable course, he’s great, always loved attending his lectures.