The ASPCA is a New York-specific group which oversees a NY law-enforcement division (you may see them on Animal Planet's "Animal Cops" show) and certain NY shelters.
I have certain problems with the ASPCA. First, I believe they waste money. Within a year's time, my household will recieve 20+ fundraising mailings from this group, all containg the exact same letter (a story about a starving dog) they have been sending out for at least 4 years, and a sheet of (often misspelled) address labels. You expect any major charity to engage in some fundraising, but this is excessive and ridiculous, in my view.
My second problem with the ASPCA is their tiptoeing around virtually every animal issue that doesn't involve pets. In order to please their conservative donor base, controversial issues are avoided. Before their website underwent a revamping a while ago, the ASPCA confined their position on the meat industry to a statement along the lines of "eating meat is everyone's choice" , making a few weak statements in support of "humanely farmed" meat, and tiptoed around the animal research issue, offering a link to a pro-vivisection group that virulently attacks the animal movement. In the early 90's, the ASPCA was criticized for partnering with the greyhound racing industry to promote adoptions of retired racers; critics said it simply lent good PR to the industry without addressing the greyhounds who are killed on breeding farms. The ASPCA also reportedly claimed vegetarians can eat chicken and fish, and fired a director in the 80s for supporting vegetarianism.
Whether the ASPCA has changed their mind is hard to know; their website instructs viewers to email them for their position on animal welfare issues.
The HSUS is the nation's largest animal-related group. Historically, they have also been slow to come out with strong positions on controversial issues, but at least they are not as conservative as the ASPCA.
The HSUS makes clear its opposition to fur, whaling, factory farms, sport hunting, cockfighting, circuses, dolphin "trick" shows and the like. HSUS spokespeople have said it is not a "vegetarian organization," something that I suspect has a lot to do with not angering its more conservative donors. However, at least its website offers vegetarian recipes and often asks readers to reduce or eliminate their consumption of animal products. The HSUS does not run shelters, but it accredits them and trains shelter workers, and publishes the shelter community's major trade magazine.
The HSUS has had good success with ballot initiatives, which it sometimes works in conjunction with local grassroots advocates to pass a measure against cockfighting or bear baiting. It is for this reason that hardline consumptive use groups often hate the HSUS...they are one of the few groups that challenge the hunter/trapper stranglehold on the political process. Consumptive users typically try to flood various companies with protests if they hear they are partnering with the HSUS in a pet-saving scheme. Most outrageously, they tried to end PETsMART's partnership with the HSUS in a program that sends vets to poor communities and Indian reservations. Sort of gives you perspective on the kill em and grill em crowd.
That said, I don't typically donate to the HSUS except when I am purchasing informational booklets or videos for distribution. I feel it is a large enough organization and has enough reserves my donation is more needed at much smaller groups like COK.
But anyway..I'd suggest visiting the websites and deciding for yourself. www.aspca.og www.hsus.org
Sorry if I talked to much, but organizations are kind of my forte.