The company has backed Michael Dell's proposal and said that Icahn doesn't have adequate financing for his plan. Shareholders will vote on the buyout offer at the company's annual meeting on July 18.
In its report, Institutional Shareholder Services pointed to the offer's hefty premium, about 26 percent over the company's share price before the offer became public, and the certainty that comes with an all-cash bid.
ISS said that if shareholders don't take the offer, they have to be willing to continue to hold shares in Dell as it continues to transform itself amid the risks of a still deteriorating personal computer industry.
The special committee of Dell's board evaluating the company's options said in a statement that it was pleased with the recommendation, noting that it believes not going forward with the sale would expose the company and its shareholders to "serious risks" that would further reduce the company's value.
Icahn said Sunday that he believes Michael Dell is trying to buy the company he founded at a "bargain price." He reiterated the benefits of his alternate proposal, which would involve the repurchase of up to 1.1 billion Dell shares at $14 apiece.
Icahn's plan would be funded with $5.2 billion in debt, $7.5 billion in Dell cash and $2.9 billion from the sale of Dell receivables. Icahn has said he and his affiliates have $5 billion in existing equity and proposed debt financing to help fund their proposal.