Mitt Romney said Saturday that a new ad from Hillary Clinton's campaign targeting him for being part of the so-called "Republican attack machine" ranks as the best part of the campaign so far.

The GOP presidential candidate took jabs at three Democratic presidential candidates, including Clinton, and a softer poke at his chief rival for the Republican nomination, Rudy Giuliani, while holding a question-and-answer session in Amherst, N.H.

"For me, I guess it was seeing Hillary Clinton run an ad with my picture in it," Romney said, describing a favorite moment on the trail. "Now, I never imagined that would happen. She said, Mitt Romney, part of the Republican attack machine. Isn't that great? I've always (aspired) to be a machine. This is really exciting to have a campaign that is that strong. She hasn't seen nothing yet, of course."

Romney was responding to a 30-second television ad Hillary Clinton began airing in New Hampshire earlier this week, which shows brief cuts of anti-Clinton ads from Republican rivals Romney and John McCain under the title "The Republican Attack Machine." The ad ends with shots of both GOP candidates' faces.

McCain has run ads in New Hampshire criticizing the Democratic frontrunner's attempt to spend $1 million for a museum in Bethel, N.Y., to commemorate the 1969 Woodstock music festival, while Romney has run ads saying Clinton lacks experience.

Romney would not back down Saturday.

"I'm convinced you are going to have the Democrats always whining about something. When we talk about their lack of experience they'll be whining. When we talk about the course they would have taken in Iraq and how bad it would have been for our country they'd be whining," Romney said. "It's going to be a lot of whining you are going to hear. But, from our side, you are going to see optimism, hope and a pathway for greater prosperity in this country. "

Romney repeatedly criticized Clinton's record on taxes, spending and health care, and doled out nearly as many barbs at two other Democrats, Barack Obama and John Edwards.

But the former Massachusetts governor was gentler in criticizing Giuliani's fiscal record. Calling the former New York City mayor a friend and "a good man," Romney said he nonetheless has "a bit of a problem" on spending and fiscal matters.

"He left a budget gap twice as big as the one he inherited: over $3 billion," Romney told a friendly crowd of about 200. The shortfall did not include costs related to the 2001 terrorist attacks on the city, Romney said.

He said the nation "needs someone in Washington who will rein in spending and say enough is enough — cutting back on the size of the government, keep it small."

In response, Giuliani said Romney is the one with a poor fiscal record.

"The problem with Gov. Romney is, he's in a glass house," Giuliani said. "Gov. Romney spent considerably more than I did ... Gov. Romney doesn't have results that he can point to as governor of Massachusetts so he then makes attacks like this."

FOX News' Shushannah Walshe and The Associated Press contributed to this report.