Tower shields and full face helms.
Our community managers at the EverQuest 2 site have updated the Guardian Class Guide with spell/skill comparisons! We're going out on a limb and pretending that they wrote this:
" Thanks to Alaric of Oggok, The Guardian's Shield now has a side-by-side combat ability comparison in Chapter 2: Abilities List. Now you can make an informed decision on which ability upgrades are worth your hard-earned gold, and which ones, well, are less so! "
You can read the entire Guardian Class Guide at EQ2.TenTonHammer.com.