FOX News exit polls from each the 15 states holding GOP primaries on Super Tuesday found John McCain the most qualified to be commander-in-chief.

But the Arizona senator may have some work to do convincing conservatives, evangelical Christians and those who consider immigration the most important issue facing America that he's the best candidate for president.

According to FOX News exit polls, the results of which do not include Tuesday's caucus states, 47 percent of voters said McCain was most qualified to be commander-in-chief, compared to 26 percent for Romney.

Among conservatives, 42 percent said Romney was their man, compared to 30 percent for McCain. Meanwhile, self-described evangelical Christians split their vote between Romney, 31 percent, and Mike Huckabee, 34 percent, while McCain got 29 percent.

Self-described Republicans split between McCain, 38 percent and Romney, 37 percent.

McCain's strength also came from independents who went for him over Romney 38 percent to 28 percent.

On the economy, 40 percent said Romney would be better at managing it, compared to 31 percent for McCain. But of those who said the economy was the most important issue to them -- about 38 percent of total voters -- 41 percent went for McCain over 23 percent for Romney.

Those who said immigration was their top issue -- 23 percent -- went heavily for Romney, 49 percent to 24 percent for McCain. For those who made Iraq their top issue -- 19 percent of voters -- McCain was their guy, 50 percent over Romney at 20 percent.Veterans went decisively for McCain as well, 43 percent over Romney, who garnered 34 percent of this vote.

The sample included 9,352 Republican primary voters.