We'll start with the manga Ami. In the BSSM manga version, Ami looked
more beautiful and her hair doesn't look like it was glued to her head
as in the anime. Her manga character was more matured and she didn't
seem that timid and it grows in every single episode, revealing the
strong and brave girl Ami truly is. It is also shown in the manga that
Ami is a studious girl and fun to be with. Not to mention that she acts
more like a normal person rather than the exaggeratedly shy and studious
girl which the anime seem to portray most of the time. Her character in
the Anime seemed so stiff and she's like a robot study machine with few
facial expressions. Gah how I hate it when they destroy such a good
character! Below are more detailed writing on the differences between
the manga and anime Ami.

Clothes
Ami has more clothes in the manga compared to the anime
where they showed her in the same clothes in nearly the whole season!
Talk about broke... Impossible! The manga clearly showed that she lived
in a mansion and in the anime she is living in a luxurious apartment, so
does that not hint you that she is rich and therefore she can afford a
lot of clothes? Everyone knows that she is rich and in my opinion even
though she does act like a studious geek sometimes, that does not mean
she has no sense of fashion at all! In the manga Ami is showered with so
many beautiful feminine clothes, but somehow the anime managed to make
her look like a peasant by wearing these ugly stone aged clothes.

Appearance
In the anime, I have to admit that Ami looked so horrible,
well in the first two seasons but later on her character and hair has
improved! In the manga she carries this air of intelligence whenever she
appeared, especially when she is serious. On the other hand, the anime
made her appear timid, shy and unnoticed. In the anime, Ami looked
rather shabby and she seemed to carry an air of
'I-need-to-study-24/7-or-i'll-fail', which is not her true appearance
and how she carries herself.

Maturity
Ami looked like the 14 year old girl that she was supposed
to in her first appearance in the anime but most of the time the anime
does not show how mature and wise she actually is. There are times that
when they were actually able to make her look mature, but most of the
time they made her look timid, giving people the idea that she is way
too shy and is nothing but a bookworm and someone that lacks character.
Whereas in the manga Ami looked wiser as she was supposed to since she's
someone with an IQ of 300... As it was rumoured.

Hair
Her hair was really beautiful in the manga, it's so flowy
(as I would describe it). In the anime her hair just looks so awful as
if it is stuck to her head! Sometimes, even though they have improved it
in the other seasons, she does have an episode or two where she looks
odd and funny.

Gadgets
Did I mention SailorMercury has really cool earrings! Three
round earrings from small to big as shown in the manga and anime. I find
that to make her stand-out from the other senshi and is her trademark.
Her visor is another unique addition to Mercury's gadgets which is shown
in both manga and anime but sadly not the little microphone which I find
to be very cute and useful in the manga.