Regular Runesmiths are basically just there to carry some Runes of Spellbreaking, as well as give MR(-2) and Forgefire to his unit. Keep him cheap (plate and shield) and hope that he gets the odd dispell off.
A Runelord is basically a Runesmith/Thane hybrid.
+55 pts for +1 to dispel, +1WS, +1T, +1W, +1I and +1A is pretty steep, but with WS6 and 3 attacks base, it might be worth investing in more than just Runes of Spellbreaking on him all of a sudden - you did pay for those increased combat-stats after all, so not putting them to use would be a waste of points. A Greatweapon with 2 runes of fury, and then either a 2+ or a 4+/4++ and a rune of spellbreaking to finish it all of looks like a decent build: most people won't expect it when your "support character" in addition to dispelling at +2 with a rune of spellbreaking on top, also whips out 5 WS6 S6 attacks and has a good save to boot.
Anvils are the actual dispellers in our army; 24" instead of 18" and with +3 to dispel, which in combination with armywide MR gives him a decent chance of dispelling spells cast by enemy level 4 wizards, especially magic missiles and assailments. Yes our opponent can play around the anvils immobility but it is what it is.
Also gives us a source of decent "spells" of our own and with PL3 they're not too shabby.
I think all 3 are viable in different ways, it kinda depends on what you want them to do:
- Runesmith: Use for buffs and RoSpellbreakinng. Keep him cheap.
- Runelord: Use for buffs and various runes. Don't shy away from weapon-runes and combat.
- Anvil: Our actual caster. Main magic-defense but also magic offense.