So far for me it's Bb but I haven't gotten to any Es yet. Nice to know I have something to look forward to?
For me, it is the G#7 chord. My little finger does not want to go where I want it to go.
We need to identify basic chords first.
Fist of all, we need to identify basic keys. My basic keys are only C and G. But I think many people think basic keys are F, C, G D and A (red circle in the figure below). Their diatonic chords are within green circle below. E is used by dominant instead of tonic, hence we don't count E as basic chord. We count E7 as basic chord (blue in the figure below) instead.
The only difficult chords come up in this thread are Bb Dm and G (yeliow circles).
I practise familiar chord sequences as a brain teaser and to get to know many keys, from 4b to 4# keys. So I encounter it in E and related C#minor key.
Like a minor sequence
C#m: 1104
F#m: 2120
G#7: 1323 (this is G7 shape moved up one fret). I myself don't find it difficult at all because little finger has an easy reach, but everyones fingers are different
What I find difficult is G#: 1343
So difficult I usually play the weaker 5343. Weaker because G# is played on 4th fret instead 1st.
This same chord is used also in Eb and Ab flat keys as Ab.
I play G# with 5343 too.
Doing 1343 is trying to do what my fingers are not meant to do.
I started to play G with my middle finger on the C string, and pointer on A. It is easier for me for almost all transitions.
But I never saw anybody to do the same.