EQ2 offers spells that upgrade in quality (now called apprentice through grandmaster) in addition to level (rank 1 to whatever the highest rank available is). The grandmaster rank (previously "Master II") is only available by a special choice upgrade - once every 10 levels or so, you can pick one spell from a list of four that gets the coveted rank.
On my Dirge, this was generally a relatively easy choice. I don't need many debuffs while soloing, so that usually crossed off one of the four choices. Improvements to my buff spells are nice, if I use the buff in question (you are limited to five from a list of something like 8-10), but the difference in any one encounter is small. Usually, this left a single damage spell, which I selected and moved on. My melee warden, on the other hand, just took his first Master II spell, and I agonized over the decision for a bit.
Choosing between roles
As a druid, my choices at level 14 included a DPS spell, a group heal over time spell, a single target heal over time spell, and my thorncoat buff.
The Thorncoat buff does damage to foes who hit the buffed target, and I always have the buff on myself. The upgrade from the basic crafted rank I was using to the grandmaster level nearly doubles the damage done. Unfortunately, it doubles the damage from like 4 to like 8. If some enemy is hitting me enough times for an extra 4 damage to add up to a significant amount of its health, this is because I am deliberately not killing it so I can work on my debuffing skills. Convenient, in that I wouldn't need to change anything I do to get the effect, but not very useful in absolute terms.
The single target DPS spell would have been a no-brainer for me if I'd been playing the class back in 2005. Today, though, Wardens don't really need to upgrade their ranged spells, because they have the option of turning them into melee attacks which automatically scale with level (and therefore don't need quality upgrades - this also makes the class less dependent on having spell upgrades ready when they level). This was actually a non-trivial upgrade to pass up - it would have raised the average damage of the spell from about 115 to about 180, but it turns out to be situational because I just won't use it.
The group Heal over time is pointless for me since I don't group. I'm not sure if it's even all that useful for players who do group - you need to have multiple party members who are injured but who will not die (or be healed by someone else) before the healing over time can take place. I have no idea how aggro mechanics work in EQ2 groups, but this also sounds like a good way to end up tanking.
This left a single target heal over time spell. I ended up picking this one, partially for lack of interest in the other options, but also because it improves my main single target heal over time spell to heal as much per tick as my small non-HOT heal does total. (The one major downside is that I'm going to be replacing this spell almost immediately, because its next upgrade arrives a mere five levels after the grandmaster choice.)
Pros and Cons of Picking and Choosing
Next tier will be an easier choice, because it will offer a large jump to a key armor buff that I need because I am soloing in melee. Still, it's an interesting little dilemma to face. You could argue that WoW talent trees offer the same sorts of choices, but it seems like you are more likely to be choosing between roles in the aggregate rather than specific spells that might be used in more than one role. It's an interesting exercise to weigh the significance of each upgrade against the frequency with which I expect to use it, even if the long-term impact is limited by my leveling past the spells in question moderately quickly.
The one other interesting spell quality decision is that players are allowed to task a new "research assistant" NPC to produce an upgrade for one spell PER ACCOUNT at a time. Many players probably assign the assistant to spend a month upgrading some key top tier spell, and I actually did task mine to upgrade my Percussion of Stone buff. This is a key mitigation ability from 10 levels back, with a short researching time due to the low level, and it does not upgrade again, so it was a relative bargain. That one done, I may assign the researcher to work on my alt's spellbook. Lower level spells upgrade far more quickly, and may have more of an impact earlier in the character's career. I can always order up some long-term spell for Lyriana the next time I'm going to go play another game and see if it's done when I get back.