I use the HiyaHiya 9" circulars and I love them. I have no problem holding them or having hand cramps. I knit socks a lot faster with them too. I've never tried two circulars. But I don't like DPNs. I was using magic loop until I tried the 9".
I say try them. The only way to know which method suits you best is to try them all and compare. Everyone is different and what works for one may not work for another, and what one person loves another will hate.
Here are some links of different brands of needles. I can't vouch for the websites as I've not ordered from them, but you can see that they are available online and get an idea of what's out there and prices. You can always see if your LYS can order them for you.
KA Bamboo 9"