I use Solo or Alpha copper foil inductors. Those are large and heavy. They avoid hysteris THD and have much greater surface area than round copper wire. They do much better with transients and are as smooth as can be. Air core round wire coils just sound sloppy next to them.
Next are the resistors. Most crossovers use low quality "sand" resistors. I use Mills MR-12's as they are precision and wirewound.
Last are the caps. I use several brands, depending on quality and cost. MIT, InfiniCap, Mundorf, etc, are all good contenders. I find some are best for the woofers, others are better for the tweeters.
Those are the most expensive parts, the coils are only a few dollars each. Then you need to assemble the bunch so the coils don't interact and transfer magnetic energy and then hot glue the mess so nothing is microphonic.
Big time pain but the sonics are well worth it. Then you realize some drivers are made very well even if the crossovers mask that.