Lib Dem leadership candidate Simon Hughes has said there are policy differences between the candidates and the contest is not a "beauty parade".
Simon Hughes has said he has an "open mind" on taxation
Hughes, who is now the bookmakers' favourite, said the race would be more than a choice of personalities.
Meanwhile, Sir Menzies Campbell denied plotting to oust Charles Kennedy.
Mark Oaten said he would consider co-operating with other parties after the election, while Chris Huhne would not seek an overall increases in taxes.
Mr Hughes, who replaced Sir Menzies as the frontrunner after his rival's poor performance in Prime Minister's Question time, said there were differences between the contenders.
Offering the healthcare as an example, he said: "There are those who believe that it is right to keep the National Health System, and the great security that gives people, as a public institution that we all pay for through our taxes.
"Whereas there are some who want to move down the road towards a national insurance, private insurance system. I reject that."
The party president has also insisted that he had an "open mind" on tax.
And when asked on ITV's Jonathan Dimbleby programme whether he had made up his mind whether to back a 50% tax on incomes over £100,000 a year, he said he would wait to hear from a "tax commission" on the subject.
"We're going to get advice. You should never have a tax that you don't need," he said.
Meanwhile, Sir Menzies, the party's deputy leader and foreign affairs spokesman, stressed that he was not involved in the ousting of Charles Kennedy.
He told BBC's Sunday AM: "I believe that I did everything in my power to try and assist him."
Mr Kennedy was right to resign, he said, but the next leader would be "very foolish" not to have him on the front bench if he overcame his drink problem.
Sir Menzies, 64, is believed to have the backing of more than a third of the 62 Liberal Democrat MPs.
Sir Menzies stressed his experience could benefit the Lib Dems.
"I believe that my qualities - experience and judgement - would be an important way of taking forward the next stage in our development," he said.
He went on to reject suggestions that his Scottish background might be a handicap to his aim of winning more seats for the party across Britain.
Sir Menzies insisted he had "no problem with Britishness" and believed voters should have "no problem with Scottishness".
Home affairs spokesman and leadership contender Mark Oaten said it was no longer sensible to use the "left" and "right" labels, and said he was also ready to talk to the other main parties about possible co-operation following the next election.
"Our liberal agenda would be the priority, but we shouldn't assume that we are the only ones with liberal values," he told Sky News.
"We should be prepared to talk to other parties if they share some of those values.
"I'm uneasy about pacts and coalitions, but I think we would have to have some kind of arrangement, because you would have a four-year Parliament. You would have a working arrangement to do the business of the day."
Mr Huhne said he would not seek an increase in the overall level of tax and Government spending as leader.
He told Sky News: "We have got to a stage - with planned increases of 41% in real terms since 1997 - where the problem in public services is not money, the problem is local control.
"There has to be much more democratic local accountability over local public services."
Mr Huhne, 51, an MP for just eight months, joined the race on Friday.
He was previously a member of the European Parliament, and acknowledged that his background made some in the party wary of him.
To stand, candidates must have the backing of at least seven MPs and backing from a range of local associations.
Nominations close on 25 January and a result is expected on 2 March, following a vote by party members.