I'll even do Last Words, too.
Hardest:
1. Minoriko's 'Autumn Sky and a Maiden's Heart' can go die.
2. Hina's midboss spell "Biorhythm of the Apotropaic God". Damn.
3. Keine's "The Legend of Gensokyo". This one fucks me up even on Normal.
4. It's a tie between Marisa's 'Asteroid Belt' and Aya's "Wind God Hidden Among Tree Leaves"/"Tengu's Fall Wind"/"Storm Day. Both are nightmares in my eyes.
5. Anything Shou or Orin uses. Argh. At least their spell cards are pretty.
6. Any of Eirin's spells on Hard/Lunatic, Kaguya's 'Hourai Jewel' or the obligatory 'Scarlet Meister'.
Extra:
Gengetu's fourth phase,
EX-Alice's homing lasers, Yukari's 'Double Death Butterfly', or Mokou's 'Imperishable Shooting'. I have yet to play against Koishi or Nue.
Last Word: Fantasy Heaven. Dear god, that's hard.
Easiest:
Stage 1: Any of Orange's attacks, Rumia's 'Night Bird', Letty's 'Lingering Cold', or Nazrin's 'Rare Metal Detector'.
Stage 2: Cirno's Icicle Fall -Easy-. Come on, now.
Stage 3: Hong Meiling's 'Rainbow Wind Chime' at any difficulty is a piece of cake.
Stage 4: The Prismriver Sisters' 'Stygian Riverside'/Lyrica's 'Fazioli Spirit Performance/"B?sendorfer Spirit Performance". Stygian Riverside is easier than its Easy/Normal counterpart!
Stage 5: Sakuya's 'Jack the Ludo Bile'. Easy, easy, easy.
Stage 6: Byakuren's "Mystic Fragrance of a Makai Butterfly" is incredibly simple.
Extra: Yukari's 'Butterfly in the Zen Temple', Flandre's 'Lavatein', Mokou's 'Honest Man's Death'
Last Word: Tewi's 'Ancient Duper' or Sakuya's 'Deflation World'
Coolest:
Stage 1: Yamame's 'Filled Miasma'/'Unexplained Fever. Swirly~
Stage 2: Any of Chen's spells, or Kogasa's 'Parasol Star Symphony/Memories' if not only for the Taito game references
Stage 3: Alice's "Benevolent Orl?ans Dolls". So pretty. That, or Brofists. Epic.
Stage 4: Marisa's "Event Horizon".
Stage 5: Any of Youmu's spells, Sanae's 'Takeminakata Invocation', or Sakuya's "Killing Doll".
Stage 6: Before Byakuren came around, I'd say Yuyuko's 'Perfect Cherry Blossom of Sumizome -Bloom-' was the most gorgeous pattern in all Touhou games. Now that Byakuren's 'Flying Fantastica' and 'Legendary Flying Saucer' are in the picture, those come in a close second.
Extra: Yukari's 'Boundary of Life and Death', Suwako's "Frog Is Eaten by Snake due to the Croak" if not only because it's a blast to play against, or any of Nue and Koishi's spells.
Last Word: Yukari's "Profound Danmaku Bounded Field -Phantasm, Foam and Shadow-" or Kaguya's 'Tree-Ocean of Hourai'.