For me it's easily refining liquid morkite. It takes forever. I swear half the team is off staring at a wall while you get the pipes built. Lastly, I can't quite out my finger on it, but the refining portion feels so scripted and boring....Every other mission type is a blast.
I find Egg Hunt to be okay if I'm playing Driller or Scout, the guys with the best transversal tools to get to the more weirdly placed eggs. I don't play it on Gunner or Engy though, it can be pretty bad (especially playing with Drillers or Scouts who like to set off the eggs as fast as possible with no pausing in between).
Hot take: but the one with the giant drill. It's really cool the first time but otherwise it's gets repetitive waiting on top of the drill until you reach the destination. The final fight also usually plays the same.
I was just playing a long ass drill mission and the host quit at the end! Ok, maybe I dislike this one the most lol. I'm taking a slow relaxed approach to the refining missions and it isn't too bad I guess.
Nooo refining morkite is my favorite! I love figuring out the best way to route pipes and then being able to ride them. My least favorite is probably mini mules, always feels like it takes forever and it can randomly go to shit from the confusing spawn triggers.
arquarqs by far. really boring mission and because I'm a gunner at heart if the right team layout is not available I can waste resupplies easily depending on map layout and area. I find vertical maps to be the most challenging think Crystalline Caverns