I started playing guitar thirty-five years ago. I wish I documented my thoughts
all those years ago. I can't recall what chords I had a hard time learning. 
Learning the banjo meant I had to learn all new chords. Many of the chords were
easy for me to learn. Some of the chords were harder. At this point I'm still 
struggling with a few chords.

Definitely, the hardest chords for me are the form V7 inversions and the 
corresponding I9 chords. My fingers hate these chords. In this example the 
chords are both D7 chords. Technically, the second chord is an Ab9 but it is 
used to play the lead note Bb with a D7 chord harmony.

A few weeks ago, Jim Riley chose a song called 'Melody of love' for my lesson.
It was a nightmare for me at first because it combined a heavy use those chord 
inversions with another problem - chord dyslexia. I have to move from an 
inversion V7 form of C7 to a III7 form of C7. Then I have to move from the V7 
form of C7 to the I form of F. Look at both the III7 form of C7 and the I form 
of F and you will see why I'm dyslexic.

There are substitutes. An alternative form of the V7 form is used often and the 
three string version of the V7 is easier to finger. But substituting these 
chords will not suffice. The key is to practice. I will be playing 'Melody of 
Love' every day for as long as it will take to be comfortable playing those 
problem chords.