From most to least disappointing
1. Shanks vs Blackbeard.
People are expecting a full crew vs crew fight when Oda is only gonna give them 2 panels at most while the rest is Shanks vs Blackbeard and a offscreen after 1 chapter.
2. Zoro vs Mihawk
Not the epilogue fight zoro fans are fantasizing about.
Oda also can't draw swordsman fights,
Zoro's best fights are with people who aren't even really swordsmen.
3. Dragon vs Imu
Standard 1 chapter of shine for the ally (Dragon) then Imu will offscreen him.
Luffy will save dragon before imu deals the finishing blow
4. Luffy vs Imu
Oda will give this much more focus since it's gonna be the final luffy fight of the series.
5.
Luffy vs Blackbeard
Oda probably planned this out more than the rest
It would be Luffy's final fight before becoming the pirate king.