Chisel tip or dual-tip — which should I buy?

If you mostly highlight blocks of text in textbooks or printouts, a single chisel tip (BIC Brite Liner, Sharpie Clear View) is faster and cheaper. If you do bullet journaling, lettering, or color-coded notes where you also need a fine line for underlining or small annotations, the dual-tip Mildliner-style pens are the consensus pick.