I have to wonder why some people are so resistant to Trigger's guide and call it biased.
Truly the god of the bolt spells, if you can get enough Magic Balance to stabilize its erratic damage range.
You're right. Totally unbiased.
In any case, I disagreed with much that he said back in the days of Ciar Adv, mainly being that IS was far more MP efficient than TH.
Considering Ciar Advance, Thunder would take at least two charges to clear a room (it can't hit the entire room at once since one charge is only 4 targets). That means it'd cost at least 70MP, or 84MP if shot twice. 59-71MP with a speedcast wand.
Ice Spear was able to OHKO on crits or with 2 charges. We'll say 2 charges since we're talking about consistency, so 64MP, or 40MP for an elf.
Regardless of race, it was possible for IS to outperform TH when the guide was written.
Cool? Definitely. Expensive and impractical? Absolutely.
Perhaps, but it really depends on how you use it. Like you said, Trigger can't think for you, and likewise I can't think for Trigger. He ranked TH first and I ranked IS first, which is why we see things differently. IS is different in that you have to keep on moving to get the best position. TH-users are probably used to corner camping, which won't work for IS.
As far as current standing goes, if you're ignoring Blaze then I honestly see Fireball as the best Advance Magic to rank. Not only does it cost the least AP, but it boasts the highest damage, biggest splash, moderate loading time, and easiest usage out of all three spells. It can hit almost entire rooms in Taillteann/Rath missions (without needing to be timed just right so everything doesn't bounce up and kill you while you stand there TH-frozen), and is the only spell capable of doing base damage on Ghasts (aside from Int). It's only flaw is that you can't really use it while soloing, but then again if you can solo it you probably won't need to nuke it with magic.