Ooh, this can be a toughie. Not to mention, my opinions have fluctuated a lot over the years...
1. Sailor Neptune -- My all time favorite!! Elegant, quiet, artsy, beautiful, and a little tragic -- she's not only my favorite Sailor Senshi, but one of my favorite characters in animation, period.
2. Sailor Uranus -- Neptune's amazing partner
I love her, as she's a great, conflicted character in her own right. Every time she and Neptune show up my eyes are glued to the screen.
3. Sailor Moon -- I love her sweetness and innocence. I love how she manages to see the good in everyone
4. Sailor Mars -- Love her fiery, sassy personality and her sweet friendship with Usagi.
5. Sailor Saturn -- Loved her in S, felt so sorry for her w/ her tragic backstory... just hate that she got shafted after the Nehelenia arc.
6. Sailor Venus -- FUNNY! Minako is so damn entertaining to watch, and I love her tragic backstory, too.
7. Sailor Mercury -- Cute, smart, and has some fun character episodes.
8. Sailor Starfighter -- He/she was nice, and I enjoyed the relationship with Usagi.
9. Sailor Starhealer -- Beautiful!! Funny and sassy, plus she loves cats like me.
10. Sailor Jupiter -- Strong, courageous, determined... she's just a little less interesting to me than the other senshi.
11. Sailor Pluto -- I'm mostly ranking this according to the anime... if this were the manga, Pluto would probably be ranked higher. I love her character in the manga, but she's so flat and underdeveloped in the anime... there's not too much there to have an opinion on.
12. Sailor Starmaker -- Meh... Her personality is ok, but I don't care for her looks or voice.
13. Sailor Chibimoon -- I'm sorry, I know it can be cliche to hate on Chibiusa... but she's just so obnoxious, selfish, and grating at times, especially in the R season, and I don't like her character design either. She does become more tolerable later on, and I did enjoy her friendship with Hotaru, but other than that... not one of my favorite characters.