Drawing hands and metal things always sucked for me. I am not really a fan of inorganic shapes that require precision and straight lines and hands...well hand are essentially one part of the human body but have the complexity of the ENTIRE human body (with fingers being different limbs and such).
However, that's not really my least favorite part.
My least favorite part is flats. I just...it's soooooooo boring. Inking can be tedious but at least I can experiment line thin and thick lines, adding crosshatching, etc. Flats is just really dull to me. Kinda like waiting at the airport for a flight. You're just there. Stuck. Waiting for the flight so you can actually FEEL like you're gonna get to your destination. I hate the flat process.