I always check out ARM chip first. Then size & aspect ratio I want and finally the brand. That is how I choose which tablet is best for me. I now include resolution since tablets no longer come with just 1024x768 and 1280x800.
Yuandao M10 - RK3188, 10.1", 1920x1200
iFive 3 - RK3188, 9.7", 2048x1536
Onda v975m - M802, 9.7", 2048x1536
iFive X3 - RK3188, 10.1", 1920x1200
First, you have to decide if you like square (9.7") or rectangle (10.1") shape tablet. People will prefer one over the other. That will get rid of half your choices. Go to electronics store and have a look at Android tablet and iPad to see which shape you like better.
Then comes down to chip, brand and tablet look since resolutions are the same.
M802 is better performing chip than RK3188 but v957m tablet appears to be little buggy. It maybe early release of firmware (kernel still needs tweaking?) or might be hardware design issue. Onda is big brand in China so less likely to be hardware problem. You have to decide if better peformance from M802 is worth less stability of RK3188. Good chance Amlogic and Onda can work out the kernel and firmware issues over next 3-4 months but hard to say for sure. So, you decide if worth the risk.
Yuando and iFive are both good brands. I think iFive is somewhat better for looks and firmware updates. I would go with iFive myself for those two reasons. Go with v975m if you want better/faster performance or go with iFive (RK3188) if you want better stability.
Always good to decide on tablet you want to buy and then read forum threads and reviews for that tablet to see what other people have to say about it. Sometimes can change your mind by doing that.
PS,
If you will do lots of (3D) gaming then forget about the 9.7" tablets you have above because their resolutions are super high and will slow things down. 1920x1200 on 10.1" is fairly high resolution too but not as bad 2048x1536.
So, if you do lots of reading, viewing images or watching 1080p video then get 2048x1536 for 9.7" otherwise for lots of gaming get tablet with lower res.