There's a good piece in The Nation explaining why Brown is a better candidate. It's available at
http://www.thenation.com/doc/20060313/nichols if you have a subscription (and you
should have a subscription). I'll quote a bit of the piece.
(snip) the Ohio story is more complicated than Hackett and his adherents would have it.
Hackett was not the strongest candidate in the Democratic primary race, and he certainly wasn't the strongest progressive. With the filing deadline for the May Democratic primary rapidly approaching, Hackett was confronted with new numbers from his own pollster that showed Brown ahead among likely voters by an almost 2-to-1 margin--46 percent for the Congressman to 24 percent for Hackett. The poll revealed that despite Hackett's full-time campaigning since last fall while Brown was tied up in Washington leading the fight against the Central American Free Trade Agreement and other Administration follies, Hackett had made few inroads among Democrats outside his southern Ohio base. Hackett has had a hard time convincing most Ohio Democrats--particularly liberal voters in the northern Ohio counties, where the party is strongest--that he would be a bolder or better candidate than Brown, who's a passionate critic of the Administration's rush to war and one of Congress's ablest critics of corporate excess.
going to be the party's Senate nominee this year not because he was imposed on Ohio Democrats by outsiders but because for all the national media attention that Hackett has garnered, Brown is the favorite of the grassroots labor, civil rights and antiwar voters whose votes are definitional in a primary and whose energy will be essential in November.
I'm inclined to believe that Hackett was a strong candidate for the House but would have had a difficult time winning Senate.