They are two different things. A "prank" is a practical joke. It is performed by a "prankster," who is said to "pull a prank." The prankster is perfectly sane, but annoying. An example of a prank phone call would be: Prankster: "This is the electric company. Please tell me: is your refrigerator running right now?" Victim: "Yes, it is." Prankster: "Well, you'd better chase it quickly, before it gets away from you! Bwa-ha-ha-ha, got you!" Victim: [uses bad language and hangs up] Another example: "Professor Jeffrey Hall got a telephone call at 5 a.m. in the morning. The caller said he was from Sweden (and had the accent to match). The caller told Hall he had won the Nobel Prize. Hall was afraid it was a prank, until the Nobel Prize Assembly posted the official announcement later that morning." A "crank" can mean an eccentric, slightly crazy person, especially one who is fixed on one specific idea. It can also mean a person who is always irritable and grouchy--"cranky." An example of a "crank phone call" might be this. "I keep getting crank phone calls from my neighbor. She is an old lady with dementia. She calls and complains that my roosters woke her up. I don't have roosters."

In my experience, prank call is more common. Either is fine though

Either works