DRM removal software. Best for Kindle?

[ratski]

I have downloaded a bunch of kindle books over time. Some I can open in Calibre, others not.

I use Calibre to convert the books to epub format to read easily on the ipad.

The ones that I can't open in Calibre are DRM protected.

I know that there are a bunch of different DRM removal softwares out there. I've used a few but none that I have tried seem to work all the time. I still get the same error message.

Anyone have any suggestions or experience?

Thanks

Dave