What key signatures are "easier" can depend on what instrument you're playing
and on whether you mean "easy to read" or "easy to sound the notes".
It may also depend on what you're used to.
On the piano, I like pieces with a few sharps or flats in the key signature
because it is easier to pass the thumb under when you are going from a black
key to a white key than going from white to white.
The C major scale may be the easiest to learn, but I find it the hardest
of all the major scales to play well.
It's also easier to strike a black key than a white key
at the upper or lower end of a chord without also striking an adjacent key,
or to strike two adjacent black keys reliably with one outstretched finger while
not accidentally striking a third key.
Once I am familiar with a certain key signature, I don't find it significantly
harder to read than C major, because I have learned through practice to
associate a note written on a particular line of the staff with a particular
key on the keyboard, which may be one of the black keys.
What is more difficult sometimes is to change
from one key to another in the middle of a piece, even if the change
is to a key with fewer sharps or flats.
But if you have only ever played pieces written in C major on a piano,
and you are suddenly presented with something written in A-flat major
(four flats), of course it will be intimidating.
Individual sheet music for some band instruments is often written in
a different key than the key in which the music is actually played.
For example, if the piece the band is playing is actually in E-flat major,
some instruments will be playing from sheet music with no flats at all,
that is, the music is written in C major but the instrument itself
transposes the notes to E-flat major.
That is, the musicians are taught to finger the instrument in a certain
way when they read the note C on the sheet music, and the actual sound
produced is an E-flat.
(Another instrument from the same series, fingered the same way,
will produce a B-flat.)
If the band actually plays a tune in C major, the E-flat instruments
will be reading music with three sharps in the key signature, and their
fingerings may be more difficult. So those instruments may be significantly
easier to play in keys with three or four flats (considering the key in
which the actual sounds of the music are produced) than in keys with
no more than one sharp or flat.