CPC_Andrew - 3:11 pm on Sep 14, 2011 (gmt 0)
Wish I had data on each source to rate them for you but I can't, I've just worked with those three a lot and know that they are simple for customers to fill out.
That coupled with the fact that those three are online shopping channels where, if you have the resources to manage them, you can make more money, is reason why I recommend them.
I think hand written requests are a GREAT idea. If you can couple that with a small discount I think your conversions will be really high.