When Allison Grant applied to business school, she did not know which of the two possible entrance exams would give her the best chance of a place. So she sat both.

The standard pan-business school entrance exam has for decades been the Graduate Management Admission Test — or GMAT. However, in recent years it has faced increasing competition from another standardised test, the Graduate Record Examinations — or GRE.

Although the GRE was designed for those seeking entrance to generalist graduate schools, more than 1,200 MBA programmes now accept it in applications. Ms Grant scored higher in the GRE, so she submitted that score in her MBA applications, landing a place at Northwestern University's Kellogg School of Management.

"People said that five years ago it really mattered that you took the GMAT," the 29-year-old former Uber executive says, "but that is no longer the case."

The rivalry between the two exam administrators intensified last month with the decision by the Graduate Management Admission Council to shorten its GMAT exam by 30 minutes.

"We didn't want to waste candidates' time," Vineet Chhabra, GMAT's global product head, says, noting that there were fewer unscored research questions in the exam.The change made the GMAT nearly 40 minutes shorter than the GRE, which lasts three hours and 45 minutes.

Exam length is a problem, according to education consultancy CarringtonCrisp, which claims that a fifth of MBA applicants are so averse to exams that they will only apply to schools where they do not have to take a formal entrance test.

"Schools are saying: 'If we can get interesting candidates we don't need to make them take the GMAT'," says Andrew Crisp, co-founder of CarringtonCrisp. He adds that the move to shorten the exam reflects another trend, noted in surveys by GMAC, of shrinking US demand for MBA courses.

The GRE was once an upstart, says Chioma Isiadinso, co-founder of Expartus, a US admissions agency. That has changed: "Many schools now track the performances of their incoming class GRE scores," she says. "We advise clients to take practice exams for both tests, then take the test that they perform best in."

Despite increased acceptance of the GRE, the GMAT may give MBA applicants an edge. A survey of business school admissions officers last year by Kaplan Test Prep found the GMAT was preferred by 21 per cent of those accepting both exams for MBA applications. Just 1 per cent said those submitting a GRE score would have an advantage over an applicant taking GMAT.

Some schools have made it harder for GRE-takers to apply. Insead, for example, previously allowed candidates to submit test results from either exam, but now accepts GRE scores only if it is not possible for the applicant to take the GMAT in their home country — it recently allowed this for a Palestinian applicant. "The long history of the GMAT test means that it is our preferred option," the school says. This bias is common among the highest-ranked schools, according to Stacy Blackman, an admissions consultant based in Los Angeles.

"GMAT is still largely viewed as more rigorous and serious," she says. "The GMAT is developed specifically for business school, while the GRE is a more flexible exam."

Judi Byers, executive director of admissions at Cornell's Johnson Graduate School of Management, believes greater competition among exam administrators is good, not only for students but also for schools eager to find more ways to assess candidates. She advises taking both tests, ideally while the potential applicant is still in full-time undergraduate study, as GMAT and GRE scores are valid for five years.

"Candidates run into hiccups with the entrance exam mainly because they have not taken formal tests for many years," Ms Byers says.

Judith Hodara, a director of Fortuna Admissions, an MBA applicant advisory service, and former admissions head at the Wharton School, says at Wharton she tried to include GRE takers to broaden the pool of students accepted on to its high-ranking MBA course.

A formal test result was only one criteria on which MBA candidates were judged, Ms Hodara notes, and not necessarily the most important.

"As admissions directors we were always looking at the overall quality of an applicant rather than just a number," she says. "Our hearts went out to those who genuinely struggled with standardised tests."

GRE takers were accepted at Wharton, but Ms Hodara admits that "the business school love affair with the GMAT is likely to continue — so learn to love the GMAT".