The big issues affecting animals: environmental conservation, endangered species protection, climate control/global warming, and factory farming. While I'm sure there are others, those are the biggies right now. While I realize I am in the minority, those issues are more important to me than the economy, or social issues.
The environment is an easy one. Obama is clearly better on environmental issues than McCain, based on their voting records in the Senate, not just their campaign rhetoric. Biden's voting record on these issues is also very good. The Sierra Club and other environmental groups endorse Obama and Biden for this reason, and compile voting records which you can search for to see the "report cards" on the issues, which you can then verify on the Senate website if you so choose. I might note also that Palin is horrible when it comes to environmental issues, to the extent she has a record on them. She is hard core "old school Republican" and believes humans come first at all costs. (If we need oil, drill in the wildlife refuge, no question, etc.)
Obama's ticket also wins on endangered species protection. Palin is a particularly bad pick for McCain when it comes to this issue, as she initiated an action against the federal government to prevent endangered species protection for the polar bear. Despite all the science and hard evidence to the contrary, and even the Bush Administration's agreement to give the polar bear endangered species protection, she believes they are doing just fine. She is adamantly opposed to their protection. Here's just one article highlighting her polar bear stance, but a web search will give you many more, including video clips on YouTube of her TV interviews. At least equally appalling, if not more so, is her support for aerial gunning ("hunting") of wolves in Alaska. She not only supports aerial hunting, but she has worked with the Alaska legislature to try and prevent the citizens from having a direct vote on the issue. (Alaska once voted to ban such hunting, which was overturned by the legislature).
Obama/Biden are also clear choices on energy issues and global warming, recognizing that there is urgency in addressing those issues for the sake of the planet. McCain, not so much. Though he claims to support these ideas, his actions and voting record do not support his rhetoric.
Here's a summary of some of Biden's views on energy and science issues, including climate control, from a group called Scientists and Engineers for America. Here is Obama's from the same group. McCain declined to answer their questions but they compiled information on his science related positions here. I might note that not answering is consistent with McCain's attempt to do only what is good for his campaign...answering questions nails you down and can cost you votes, while leaving things open creates ambiguity and maybe you'll keep some votes because voters make assumptions about you.
Particularly disturbing to me is McCain's taking this attitude all the way in failing to show up and vote on key alternative energy legislation. He was in DC when a key vote was taken but failed to show up, and so the measure failed by one vote. (Obama was present and voted for the bill). McCain had a chance to do what was good for America and support wind power and alternative energy but he took the easy way out and supported the oil industry by failing to appear - he would have made the difference. He did what was good for the campaign - remaining ambiguous - as he can now claim he supports alternative energy despite his abysmal lack of ever doing so on the Senate floor when it actually counted. He has actually missed EVERY energy vote on the Senate floor, more than 11 in all. His talking points are just that - his action is to not show up, not cast votes that matter, and not get serious about energy policy in a meaningful way.
Palin is another example of a choice me made that is good for the campaign and not the country. Seriously, he could hardly have found a less qualified candidate, and for someone 72 to not put the best interests of the country ahead of trying to win the campaign is pretty repugnant. I know he wants to pick up the religious right and since she is exceedingly religious and has positions in line with the hard right she helps him do that - but it undercuts any moderate stance he might have been trying to pull off.
As for factory farming, neither candidate has chosen to make statements about seriously changing this. Obama did at least bother to respond to questions about it, and while I don't particularly like his failure in his response to address humane conditions for animals, at least he responded. As usual, McCain didn't. Had he, the typical Republican platform is to support CAFOs and justify factory farming conditions with responses about the economy and ignore the animal issues. However, he would like to leave this too ambiguous, it appears.
While I have never considered myself a Democrat, I have to say that this election I clearly can't support McCain, even without the hideous addition of Palin. While Obama has not expressed the concern for animals I would like in a candidate, I understand the political reality that he has to address the issues that concern most people, not the fringe issues. Sadly, animal conditions remain a fringe issue at this time. But, at least he bothered to respond to questions, and on the big environmental issues he is definately a strong choice.
It will be an exciting election. I do think it's a great sign that finally both parties had a moderate candidate instead of the extremes that usually come out of primaries. Can you imagine a race of extremes with Hilary Clinton v. Mitt Romney? We'd want to kill ourselves with choices like that. At least this way, we have two relatively moderate choices. Unfortunately, McCain is swinging to the right, and Palin particularly skews things hard right. If more people participate in primaries, we can select less hard core extreme candidates, a step in the right direction.
Now we sit back and wait to see how it all plays out.