I think Ignatieff would be horrible for the Liberal Party, and Canada, but good for the NDP, because of his neo-conservative foreign policy, and pro-torture views, that would put us even more inline with the US then Harper. He'd probably create space of the centre-left for the NDP, but should he still win, again he'd put Canada more inline with the US government. He's also the least experienced, and would be the most likely to make mistakes, not to mention the fact that he comes across as arrogant and condescending. He has absolutley no common touch. Also, intrestingly enough, though this really shouldn't affect his candidacy, most of the Liberal establishment is backing him for leader. If they end up managing his campaign, like they did Paul Martin's...we'll I'm just saying. He's elquent, but I don't think that's enough.
Rae was a horrible Premier, with a lot of skeltons in his closet. Otoh, he's the only one with experience leading a government, and an official opposition. He's a good speaker, but he's probably only slightly less despised then Mike Harris, so that's not really enough. Otoh he wasn't overly weak anywhere in the country, although as was expected he was slightly weaker in Ontario then the rest of the country delegate wise.
Kennedy had an embaressing showing in Quebec, and his French isn't very good. Otoh, his support was relativley uniform throught the country, and unlike Dion he actually managed to win a province, Alberta (although that was amongst Liberals, so it's not likely he'd nessecarilly win more seats). I don't think he stands much of a chance though.
Dion is probably the best of this lot. He's not a great speaker, in English. But he's not really connected to the Sponsership scandal, even though he was the only one around. Some say he's too controversial because of his hardline federalist views, but that should solidify the Liberal base in Quebec, and he doesn't have as many negatives as Rae or Ignatieff. Even though he and Kennedy are probably the best Candidates, neither stands a chance unless one drops out infavour of the other.