|Level||Attack (av. +3/lvl)||Defense (av. +0.5/lvl)||Damage (av. +2.5/lvl)|
The Rod of Ruin is one of the most popular weapons and a common first epic craft, owing to its fairly minimal artisan requirements (available at level 40) and being a safe end-game investment for relatively few void cores. In spite of being only tier 1, it vies for the highest damage staff in the game due to the double damage-type bonus, causing its DMG stat to be double in value. Available at level 55, the Eye of Chaos far outclasses this weapon.
While ideal for the Archmage, the Rod of Ruin is arguably even better on the Mage. The Mage is faster, allowing him to proc the Staff's large damage bonus more often. He also typically has ~2 more stars, which makes up for his lower base stats. The Eye of Chaos has a 35% speed boost -(plus bonus true, lightning and cold damages), so it brings the Archmage up to, and WELL above par.
The Rod of Ruin can even be used for the Druid, who can deal respectable damage through her offensive skills and passive. This is most common when the Druid's area healing from her soul skill is desired, but the player doesn't want to compromise offense, such as in double healing compositions using the Cleric, Druid, and Knight which have low offensive potential. The Chaos Staff does have an extra Wrath of Nature in its bonuses-but it's offset by the Druid's inability to heal when equipped with this Staff.
The Spellthread Robe is very effective when combined with the Rod of Ruin. The Spellthread Robe boosts all magic damage (except poison) by 10%, effectively making the damage bonus on the Rod of Ruin 10% stronger, or 20% on Light, Cold, Lightning, Shadow or Fire attacks. Chaos Staff is even better for this with its triple bonus.
The Rod of Ruin is extraordinarily useful in PvE, and if acquired early enough is devastating in tower PvP. It singlehandedly makes basic stall floors useless(, and nearly one-shots squishy defenders). In tower defense, with Chill Turrets and/or taunts/walls to buy time, a well-starred Archmage with the Rod of Ruin will obliterate any attacking team without super rare or better armour. Even against good armour, it can soften them for a follow-up floor.
At the highest levels, the Rod of Ruin is less explosive. Opponents all have end-game armour, while the Rod's best wielders fall off, the Mage due to lower base stats and the Archmage due to slower cooldowns relative to the Warlock, who acquires a more powerful weapon in the Wand of Endless Suffering (albeit with artisan requirements for level 45, making it less feasible as an early craft). Nevertheless, in PvE the Rod of Ruin remains a great investment throughout the end game, especially in the hands of an Archmage with high stars.
It is possibly outclassed by a max-level tier 2 staff, the White Staff of Viarus, which at max level deals comparable damage while having far superior defensive stats. BUT, there's no more superior staff than the Eye of Chaos. Invest in it and it will do wonders, though it is a level 55 weapon. Bonus true/lightning and cold damage as well as a speed boost make it the perfect Staff to replace the RoR.
(The best counters to the Rod of Ruin are high defense and especially high magic resist, both of which are most easily obtained through high-level armor, or through skills such as the Cleric and Warmaster passives. Area healing like the Druid can also be useful.) The RoR, while still useful, is far less effective against newer level 55 gear.