There are two mainstream ways of building a guardian: a rock or a sponge.
A sponge usually has very high morale and mits, average BPE and nothing else to show for. His job is to just spam taunts and soak damage. Because of the lower BPE, he puts some strain on the healer, but the higher morale pool also makes it more forgiving when a healer is stunned. On power draining fights such as the LT of DG, this type of tank is a pain to keep alive. It only became a really viable build when the whole threat mechanic was scrapped and taunts were buffed (permataunt).
A rock is a tank who focuses on maximizing all other defensive stats, some offensive stats and only then morale. They cap their mits and BP, get their E and Res very high, aim for 50% CritDef and also invest in Might and Finesse instead of just secondary stats. Once those stats are okay, they fill all other slots with morale. The idea here is that they take less damage through high avoidances and mitigations, giving healers an easier time. They also focus on outgoing damage and finesse so they can't wipe because a skill got resisted or missed. The added bonus is that they output way more damage than a sponge, facilitating the fight because the boss dies faster.
An extra benefit to being a sponge is the insane amount Warrior's Heart heals for. The flip side is that rocks can tank a lot of mobs for a long while without needing heals. Also keep in mind that in Dome of Stars, a lot of mobs have skills that remove 80% of your max morale. This basically turns sponges into 10k morale squishies, while rocks become 7.5k avoidance beasts.
I like this comparison because the analogies match: a sponge can absorb a lot but hardly hurts when thrown at your face. A rock is sturdier, but hurts like hell when on the receiving end of a throw.
I chose to be a rock. As such, I run with (off the top of my head; will correct later):
- 37500 morale
- 26% Block (including 5% skill tree)
- 25% Parry (including 5% skill tree)
- 17% Evade
- 61% Physical Mitigation (1% Dwarf)
- 60% Tactical Mitigation
- 50% Critical Defense
- 25% Incoming Healing (including 5% skill tree)
- 25% Resistance
- 15% Finesse
- 40K Physical Mastery
P.S.: Keep in mind the investment to get B/P/E to the actual cap (25%) is insane compared to the rating needed to get 20%. This is why many people consider 20% as the cap for B/P/E and boost their B/P with the 5% bonuses from class points. Critical defense over 50% is a waste as well, seeing as anything above it only affects the magnitude of devastating hits. Finally, you need to overcap your mitigations by a rating of 6750, because of T2 mobs penetrating your mitigations by that amount.