2. The "Kes"
You get to play one of the major characters in the series from day one - brilliant effort - and the makeup isn't that strenuous if we're honest - a bit of a blonde Beatle wig, add in some larger auditory orifices and you have your very own Ocampan; a somewhat elfin creature with a seven year lifespan. When you get into the third season there's a nice revamp of the character because you're not hitting the mark somehow - you get some new togs and also get rid of those ears by letting your hair down. Not only does this make Kes look a lot more grown up but also means she has nothing about her that distinguishes her as an Ocampan. Very clever bit of time and money saving there which would only last for a few more episodes. At that point Jennifer Lien was cut and replaced by Seven of Nine who also could be classed in this list with her couple of token and non-distractive Borg implants carefully placed.
Reminds us of: Seven's Impact on Voyager