10 Lothario
Don Lothario has been in The Sims franchise since The Sims 2. And though his looks and other things have changed about him, what hasn't changed is his flirtatious nature. In The Sims 2, Don is in a relationship with both Caliente sisters, a maid, and Cassandra Goth, who he's supposed to marry. He always comes with a Romance Aspiration, which makes him want to romance as many sims as he can.
The same is true for his newest iteration in The Sims 4, which has him living with the Caliente family. The family bio suggests that he's moved in with them as Katrina's (Dina and Nina's mother) boyfriend and that he wants to be involved with the two sisters as well.
9 Caliente
First appearing in The Sims 2, twins Nina and Dina are alluded to be connected to Bella Goth's disappearance in The Sims 2. Both sisters are (unknowingly) dating Don Lothario and Dina is in a relationship with Mortimer Goth and plans to marry him, though most think it's only for his money.
The sisters are apart of a family that includes an alien lineage as their grandfather was abducted by Pollination Technician 7 which resulted in their father Flamenco. The sisters come back in The Sims 3 with Barnacle Bay and are joined by a friend of theirs Luisa Libros. In The Sims 4, we get alternate timeline versions of them, living with Don and their alternative mother Katrina.
8 Burb
The Burb family is another family that was introduced in The Sims. The family of four, Brad, Tiffany, their son Johnny and the family dog Tucker, came to be in The Sims: Unleashed. The family moves from the big city to Old Town, as father Brad is tired of the city. Though his wide Tiffany isn't. The family is seen again in The Sims 2, with an adult Johnny, who now goes by John.
John moves back to the Pleasantview with his wife Jennifer and daughter Lucy. The Burbs also make a return in The Sims 3, though with just John and Jennifer. Wanting to sail around the world before they got married, the two managed to get themselves stranded, in Dragon Valley of all places!
7 Broke
The Broke family is a pre-made family from The Sims 2 made up of 4 Sims. Brandi Broke lives in Pleasantview with her two sons Dustin and Beau and with another baby on the way. Brandi is a widow whose husband, Skip, died in a "suspicious pool ladder accident" and is left to raise her sons. Her oldest is Dustin who is a rebel in the Criminal career and is dating Angela Pleasant.
The Broke family is also in The Sims 3 in Riverview and features Skip, his parents, his sister and his uncle with his two kids. The Broke family (like their namesake) are usually one of the poorer sim families. Dustin also seems to have an alternative Universe version of himself in The Sims 4: Get Famous.
6 Goth
The Goth family has been so prominent within The Sims franchise that one can think of them as unofficial mascots for the series. If you've been playing the game for a while, chances are you'll recognize Mortimer, Cassandra and of course, Bella Goth. The Goth family has been around since The Sims and has been featured in all four main games and a few of its spinoffs.
In the game's lore, they have a long lineage of wealth, and sometimes a magical lineage. Mortimer has always been featured in the game, with Bella a close second and then Cassandra and Alexander. They have one of the largest family lineages in the franchise as well.
5 Pleasant
The Pleasants is another family that has been with the franchise since the beginning. They first appeared in The Sims as one of the starter families for players. Made up of Diane, Jeff, Daniel, and Jennifer, the two kids (Jennifer and Daniel) are adults in The Sims 2 and are both married.
The way most players probably remember the Pleasant family is from The Sims 2, as Daniel marries Mary-Sue Oldie and has the twins Lillith and Angela. Mary-Sue and Daniel appear in The Sims 3 world Sunlit Tides as newlyweds on their honeymoon. With the most recent Expansion Pack, The Sims 4: Discover University, the Pleasants are back, with Angela and Lilith, who live together in a family home in Briechester.
4 Dreamer
The Dreamer family first appeared in The Sims 2 in Pleasantview. Initially made up of a father and son Darren and Dirk, Darren is a widower who has set his affections on Cassandra Goth. And Dirk is his teenage son who has been childhood friends with Lilith and is dating her. The Dreamer family is one of the less wealthy families in the game, and they start off with owing three different overdue bills.
In The Sims 3, Darren is a sim that comes with Lucky Palms who is a much wealthier celebrity artist. The Sims 4: Get Famous also has a Dirk Dreamer who is a 4-star celebrity in the Tech Guru career. It's assumed that this Dirk is the alternate universe version of Pleasantview's Dirk Dreamer.
3 Newbie
The Newbie family has always been apart of The Sims series in some shape or form. First seen in The Sims as Bob and Betty Newbie, they were the tutorial family used to introduce new players to the game. In The Sims 2, the Newbies are already dead and can't be played, but Brandi Broke is their daughter meaning the Newbie lineage continues on with Brandi and her children.
They are playable in both The Sims 2 and The Sims 2 Pets for consoles and were given a dog named Buddy for the Pets console. They are available in the Family Bin in the Sims 3 for Riverview. Back in February of last year, Maxis made an official recreation of Bob, Betty, and Buddy for The Sims 4.
2 Bachelor
The Bachelor family is one of the 3 iconic starter families in both The Sims and The Sims 2. Micheal has a connection to several iconic characters in the franchise. It isn't revealed until The Sims 2 that he's Bella Goth's brother. He appears to be her older brother as he is a deceased elder in The Sims 2 and a teen in The Sims 3 while Bella is a child.
He's the late husband of Nina Caliente in The Sims 2, though a 'bachelor', like his namesake, fresh from college in The Sims. The only rendition we haven't seen of him (so far) is in The Sims 4.
1 Landgraab
Another notable family in The Sims franchise is the Landgraabs, who have been here since the beginning, just like the Goth family. Also like the Goths they are one of the richest families in the game, though where the Goths gained their wealth through successful businesses, a big part of the Landgraab wealth seemed to come from less than legal practices.
The Landgraabs (or Landgrabb as in The Sims), are first made playable in The Sims 2: Open For Business. In The Sims 3, the Landgraabs reside in Sunset Valley, a town that the family took part in founding with the Goths and are enemies with the Alto family. In The Sims 4, the Landgraabs still have a criminal background, as Nancy is a career criminal, though Geoffrey is a secret agent.