SAN FRANCISCO, USA: Will Hewlett-Packard Co's most important competitor in the next decade be Apple Inc, Cisco Systems Inc or IBM? Look to its choice of CEO for the answer.

Although the controversy over Mark Hurd's resignation is likely to percolate for some time, investor attention is already shifting to the future as the world's No.1 PC maker searches for a new chief executive and chairman.

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Many analysts are betting HP will go outside its ranks to pick a new leader to ramp up topline growth, as it did to hire Hurd in 2005, and Carly Fiorina in 1999.

Whoever it picks will have big shoes to fill: while Hurd was ousted for allegedly fudging expense reports to conceal a relationship with a female contractor, he was well respected on Wall Street and credited with reviving HP's fortunes.

Since he took the reins in 2005, HP's market value has more than doubled to roughly $100 billion. Hurd's tenure saw one of Silicon Valley's most iconic firms become the world's largest tech company by revenue.

But given HP's size -- it is a sprawling company with more than 300,000 employees -- ramping up top-line growth will be a challenge for whoever succeeds Hurd.

"Whoever they name as a successor, investors are going to read that as a signal for the direction they're taking," said Stifel Nicolaus analyst Aaron Rakers.

HP's most direct competitor is arguably now International Business Machines Corp (IBM), which like HP sells hardware, software and technology services to the world's biggest companies. Several IBM executives including Steve Mills have been cited by analysts as potential CEO candidates for HP.

But HP also faces a new rival in Cisco, which is trying to get into the computer server market to complement its network equipment business, and run all aspects of the corporate data center. If HP pursued someone like Cisco Chief Strategy Officer Ned Hooper as CEO, that would be read as a sign it planned to move aggressively into the network gear business.

Last but not least, Apple is also emerging as a fierce rival for HP as the popularity of the iPad threatens to redefine computing, while the iPhone continues to win market share in the mobile market.

As HP prepares to enter both the tablet and the smartphone market following its acquisition of Palm Inc, Apple Chief Operating Officer Tim Cook has been floated by analysts as potentially an ambitious hire.