There are at least three different film versions that I know of, so I'm not sure if you have a specific one in mind. For the most recent version, in which Sean Combs plays Walter, here are a few key differences:
The movie version leaves out two important scenes from Act II. The first omission involves Beneath and Walter in scene 1; the second involves Mrs. Johnson in scene 2. It adds a scene in Act II where the family visits the house in Clybourne Park. It also makes significant changes to the conversation between Beneatha and Asagai in Act III.
While the movie does include Beneatha putting on the African robes she has been given by Asagai, playing the African music, and dancing around the apartment as she does in scene 1 of the play, she is never joined by Walter on his "drums", nor do they shout "OCOMOGOSIAY" to each other. This is a great scene in the play showing Beneatha and Walter coming together, caught up in the moment as they "travel" in their own ways to Africa, where they are admired and respected. Additionally, in this same scene in the movie, Beneatha never cuts her hair short in an effort to be less "assimilationist," as she does in the play.
In the movie version, another key omission is that Mrs. Johnson never comes to visit the apartment. In the play, she comes with her newspaper and the news of another bombing:
Johnson: …I guess y’all seen the news what’s all over the colored paper this week…
Mama: No—didn’t get mine yet this week.
Johnson: (Lifting her head and blinking with the spirit of catastrophe) You mean you ain’t read ‘bout them colored people that was bombed out their place out there?
Her primary concern in this visit, other than seeing if there is any new gossip, seems to be to instill fear in the Youngers and criticize them for choosing to move into a white neighborhood. Beneatha, in frustration, later complains to Mama that there are two things that the Black community needs to overcome: one is the Ku Klux Klan, and "the other is Mrs. Johnson." She recognizes how timid and fearful attitudes such as Mrs. Johnson's will keep the Black community from being able to move forward.
One scene the movie adds is that it shows the family going to visit the new house in the white neighborhood. It is there, in the movie, that the family presents Mama with her gifts (in the play, this happens in the apartment). The movie also depicts the neighbors watching them from behind their curtains, and finally Beneatha shouting "Howdy-doo" to the furtive onlookers. She shows that she will not be intimidated.
A significant change is in the conversation between Asagai and Beneatha at the beginning of Act III. The movie cuts out a lot of their political discussion. It also has Beneatha blame Mama more than even Walter for the loss of the money, saying Mama should never have trusted Walter with the money. It is up to Asagai, in response, to say that perhaps Mama sees things that Beneatha doesn't - such as Walter's need to feel empowered.
As for preferences, I like that the movie includes the family's visit to the house; I wish that it did not leave out the scenes from Act II. In general, I prefer watching the movie because it brings the story to life. Plays are truly meant to be performed - and the print version of the play has so many italicized performance notes that it really slows down the story's action when reading it.