As a philosophical point, I'm curious - do GURPS GMs, especially GURPS Dungeon Fantasy GMs, prefer to place magical treasures that enhance PC defense, or enhance PC offense?
I personally lean towards offense.
PCs with a good offense can deal with more and bigger and deadlier monsters. Increased offense allows them to threaten foes they couldn't otherwise easily threaten. Or maybe threaten at all, given appropriate immunities or powers. Even if only one or two PCs can threaten a foe, they can - as a group - confront such a foe.
PCs with a good defense, however, can neutralize monster's attacks. They increase the whiff factor (if literally improve defense) or reduce the effect of hits (if DR). In order to get such PCs to feel some concern in combat, monsters have to get tougher. Every increase in defense on one PC means more, stronger monsters are needed to threaten that PC. And thus all of the other PCs need to keep up . . . or the GM has to keep up, or both.
So I tend to think it's better to give out artifact-level offensive items over letting out even moderately-powerful defense-enhancing items. You'll see some magical defenses in GURPS DF Felltower, but a lot more power offensive weapons. For every suit of awesome plate or mage-scale, or protective ring, or set of armor-providing bracers, you'll see 2-3 magical weapons or offense-enhancing items of equal or greater potency.
How about in your games?