I'd be happy to answer specific questions about specific curricula that I know about, but I haven't used most of them, so I can't answer all your questions.
And I second Dottie's motion for you to go easy on yourself about the curriculum. Have you read the "Least worst option" article on Hoagies? It helped me to relax. I think I mentioned it to you before, but if not, try this:
http://www.hoagiesgifted.org/least-worst.htmMostly I'd recommend poking around the math providers' websites. Some have free trials (Aleks) or sample pages online (Singapore) for you to check out. Once you have narrowed your search to a couple of contenders, buy one book/one month of both curricula and try them both out. Then stick with the one that your child seems to work best with.
Dottie's right, too, about the way to start narrowing the search. Start by thinking about whether you want a primary math curriculum or supplement, and then decide if you want your child to go online or use a workbook. To me, that's the simplest way to cut the number of possibilties fast. From there, it's just personal choice and what works for your child, as well as cost.
If you haven't committed great amounts of money to a math curriculum, then you can always dump it if it stops working and try something else. We loved Singapore for 6 months or so, but it hasn't been working for us lately, so we're shifting gears. No more Singapore for us for now, but we're starting to do some higher level geometry than 6yos usually get. (I just found a book I liked at the library for that. No workbook. Just me and a textbook that looks good.) I didn't invest in the full Singapore curriculum, so the switch is no big deal.
If the geometry doesn't fly well, we'll try something else. <shrug> It's not a big deal. He's learning all the time anyway, so I'm not too worried about it.
And BTW, math is NOT my subject. But at this age, there's just no need to worry too much about it. As long as you teach some math and you respond if the choice doesn't seem to work for your child, there's really no "wrong" choice.
It's not as hard as you're making it, squirt. I promise!