1. Spell deals 5000 damage over 30 seconds.
2. Spell deals 500 damage every 3 seconds for 30 seconds.
The advantage of Option 1 is that, while it doesn't tell you exactly how the damage is dealt, it gives you the total amount, making it easy to compare damage-per-cast-time to other abilities. Given that DPCT is the most useful stat for ranking spells, this is a useful format. Option 2 requires you to multiply and divide to get the DPCT.
Option 2 tells you how much each tick is worth, which is useful if you won't get the full duration of the effect. This often happens with area DoTs like Rain of Fire, where people run out. As well, heals and shield hots (the new Sacred Shield) might have wasted ticks when the target is at full health, so knowing the tick amount can be more useful than a total number which is only partially used.
Option 2 also gets less useful when the damage dealt per tick changes. Like the new paladin spell Execution Sentence or the old warlock Curse of Agony. With Option 1, you can just tell the total, and add a rider saying that the damage increases as the time goes on.
Which tooltip do you prefer? Or do you have a different form that you'd like to see?