I don't know what to vote for really!
Personally for me, the hardest skill to learn was I suppose the bhs because I was really scared of going backwards but once I had it it was easy - also a simple squat on on bars! I really found that hard! (I was a very low level gymnast, didn't compete or anything!)
Now, to coach, It depends on which level of gymnast I am coaching.
I actually find the more advanced skills easier than some of the easier ones - Cartwheels are really hard to teach to complete beginners!
I'd rather teach a tsuk or yama****a than a handspring vault!
I also find teaching back somersaults hard, to someone who has never done them before!
So overall, like I said at the beginning, I think it is the easy skills which are often the harderst to teach!
For Bean, it was giants. She has really small hands and it took awhile before both she and her coaches felt comfortable letting her do them unspotted. It was almost 7 months from when she started learning them, until they were competition ready. In a competition video from last February, you can actually see her coach getting all "mother hen" and ready to jump in and save her. Lol.
Teaching FHCs with straight arms is possibly my least favorite thing to do in a gym. I don't like the skill to begin with (I'd rather spend that time working tap swing shapes and kips), and it's really spotting intensive if you don't want them to go to their ribs.
For me, BHS BHS on beam was hard... not so much physically, but definitely mentally. A lot of kids are scared of missing their hands, but I'm the gymnast who actually DOES miss her hands. Bails took the longest to learn because I tried to turn the wrong direction for 4 summers, but I'm not sure that counts.
on bars- either the geinger or tkatchev. or the jaeger. toook me forever, same with my kip haha.
beam- back tuck. i would always fall, and it took me at least a year to consistently stick it.
floor- double pike. i'd always throw it too hard and land on my butt.
BHS on beam were terrible for me. I was terrified of beam to begin with and even after doing BHS on the high beam for several years, it just never got any easier or any less scary. I would just chuck it and hope for the best which is a terrible philosophy but I didn't know what else to do. And bwo-bhs and bhs-bhs were not so great as a result of it.
I think some of the easier skills are the hardest to teach. Some kids just do not get round offs no matter how many drills you try. Like gymkat said, FHC are also terrible. I come home sore, frustrated, and with my mind repeating the same corrections over and over again. When I'm teaching beginners up to new level 4s handstand forward rolls with straight arms are rough. Just getting them to hit a handstand at all before rolling can be a challenge.
On that list - my back full. I am a horrible twister. I flip much more easy than I twist. From there, my full-in's were difficult because of the timing of the twist into the second flip. But after I got it, it became one of my favorite skills!
I voted BHS on floor and handstand static hold. My BHS took me about 8 months to get, a ridiculous amount. My handstand hold is only really just starting to click. I just can't seem to stay up for longer then 3 seconds!! Any tips?
Heh, should've put roundoff on there... I have issues with leaving my head out and not going over the top. I think they're getting better, though.
I said my kip... that took a long time, but my flyaway would definitely take the cake! It took me MONTHS. I was such a headcase about them. Almost drove me to the point of quitting, honestly. I just hated going backwards... it was really pretty nerve-wracking to me. Now that I'm an optional though, I can front flyaway and that has been wonderful!