General guidelines on choosing weapons:
1. If the build is reliant on enchantments, use a staff of the main attribute with 20% enchant length and 40% half cast time.
2. If the build is not reliant on enchantments, use a wand and focus of the main attribute with 40% half cast time and 40% half skill recharge.
3. If the build uses more than one attribute, pick the most important attribute OR use a staff with universal 20% half skill recharge.
Example: Discord Necros. The build has no enchantments so definitely don't want the enchantment mod. The spell you most want them to cast is Discord + you usually spec 12 into Death Magic, but since the Necro will usually be holding Kaolai any HSR mod for Death is not likely to matter. The best weaponsets then would be a 40/40 Restoration set. You can also use a Death Magic staff if you usually push so hard your red bars are constantly dropping, which means heroes will drop Kaolai.
Example: Prot Monk. Protection spells are usually long-lasting enchantments, which immediately means you should use a 40/20/20 Protection Prayers staff (#1 of the guidelines).
Example: Spiteful Spirit Nec. It depends to some extent what's on the rest of the bar. If the SS Necro is responsible for casting Protective Spirit and Aegis, then you need the enchanting mod, and the best choice is a 40/20/20 Curses staff. If the SS Necro has Restoration heals on the bar, then again the hero is most likely to be holding Kaolai in fights, so a 40/40 Restoration set is best (or a Curses staff if you find heroes usually aren't holding Kaolai). If the hero has nothing but offensive spells, then a 40/40 Curses set is the best.
gl and hf