I like runestaves for spells that you only sometimes want. Dimension Door and Teleport are a good example there. I also like the Runestaff of Evocation, especially since it uses your caster level when you power it up, so you can get decent damage out of it. I find that evocation blasts are not often needed, but on occasion are exactly what you want in some quantity. Spells that fall into that category are great for wizards to have on a runestaff. For a sorcerer, OTOH, runestaves that mimic useful spells are all-around great, since you can get past the whole spells known limitation that way. They're all great, and if you can custom-design one, they're amazing. The one problem is they're nigh-impossible to craft yourself (craft staff is a lousy feat otherwise, and you have to know the entire spell list of the staff, which kind of defeats the purpose). That means no discount on the staff, which is sad.