RE: Worst part of assembling an ARF is....
World Models took all the work and guessing out of cutting cowls with their "3-D" plastic cowl.
In general, the cowl work really shows your attention to detail and your level of skill, after all, it's the only part of the ARF you really heve to do some work on. I hate to see a cowl on a plane that fits poorly, cut poorly and has jagged edges in the cutouts.
The part I dislike the most is setting up mechanical retracts. The best retracts I've had to set up were on a World 60 size Spitfire, they worked and looked great.
OH YA... painting canopy frames sucks too.