So you got an Xbox/Wii/PS3/PS4/Xbox One but don't know which motion sensing dance games to buy. It can be a difficult decision being that there is almost an over saturation of dance games for all the current and last generation consoles.
I personally prefer the Xbox 360 and Xbox One as I find the motion sensing via the Kinect and Kinect 2 sensor are far more superior to the other consoles motion sensing peripherals.
Aside from that, Dance Central and Just Dance have some differences but are similar in many ways. Just Dance is more suited to those wanting to just have fun. Dance Central is more suited to those wanting to learn how to dance.
Dance Central is developed by Harmonix, who previously created the Rock Band and Guitar Hero games. Just Dance is created by Ubisoft which isn't quite known for their music or rhythm games.
Dance Central has been claimed to be the best selling dance game series so far. Dance Central was also one of the launch titles when the Kinect sensor first came out (previously called Project Natal when in development).
Just Dance has a pretty big following as well, with the first few games only being released for the Wii (later released as Greatest hits on other consoles). Just Dance is available on all current and last generation consoles. Just Dance has even released games for the PS4 and Xbox One (so far dance central has been shelved and is not in development for current systems).
Dance Central is more realistic and has more variable difficulty. Songs in Dance Central are graded from 1 to 5 stars based on difficulty. You can also choose individual difficulty for each song as well, ranging from beginner to hard. As you progress through the lower difficulty moves you can move onto the harder difficulties to try it out.
As the difficulty for the song is increased (by the player's choice), the moves become more difficult and faster paced. They also build upon previous difficulties dance moves, with hard difficulty incorporating moves from easy and medium with new added moves. One minor drawback to Dance Central is that the dance moves don't always flow as much as they do in Just Dance which I find to be a minor setback.
There is also a practice mode In Dance Central you can use to practice moves of a particular song. You can slow down the song, practice certain parts practice the whole song in practice mode.
Just Dance on the other hand doesn't have any practice mode. Most of the songs have normal or hard difficulty and most songs are typically faster paced (more of a workout if that's what you are looking for). Just Dance has flashcards for the upcoming dance moves scrolled across the bottom (going right to left) as you dance to the choreographed dance of the onscreen character to the song you chose.
Dance Central uses a similar system but has flashcards with the names of the dance moves, scrolled from bottom to top on the right or left side as you follow the on screen dancer/character dance to the song.
Just Dance allows you to unlock songs using mojo points (and in Just Dance 2014 Xbox Live points, Wii points/ PSN points) to unlock new/alternate dance routines for songs, mashups and battles. You can also download new songs via points or money (depending on system you are playing on).
In Dance Central you have the option of importing songs from previous dance central titles as well as new songs via DLC with points or money. With this you can create quite a large library of songs on one game with up to 100-200 songs on one game. With Just Dance you typically have to change game discs to get more songs or play different songs.