Which muscle grow the easiest, or just don't respond and are lagging and why do think this is?
For me:
Best bodyparts:
Tear drop muscle

Rear delt

Worst bodyparts:
Triceps
Hamstrings
Calves
I think my triceps and hamstrings lag because I train at home with free weights so don't have access to machines to isolate the muscle.
For example I can really feel the contraction in the triceps with the tricep pushdown machine, whereas I cant feel anything with free weights.
Squats and deadlifts don't seem to do shit for my hamstrings, so I would probably need to use the leg curl machine to bring them up.
Calves I've basically given up on at this stage of ever getting them big, so I just go for walks where I focus on the contraction of the calves trying to keep a constant burn going. This keeps my calves in shape. If I stop walking I will lose an inch on my calves over time. Again I have no access to a calve raise machine.