The 20MP one would be the best and give the best first step from analog to digital content. I use an ION unit, but it isn't much over 5MP. It yields files that are almost 5 MB .JPEG files, larger than most e-mail systems. I prefer the largest file possible for the first conversion from analog to digital. I can always reduce the size and resolution to suit my needs. The ION has a holder for 6 negatives and another for three slides. Whatever device you choose, select the maximum resolution to get the most content and manipulate it later. There are many businesses that will do the conversion for you but that gets difficult identifying exact images on a strip when you only want one image out of many. I've done close to 2,000 of my negatives with about that many left. I've only transposed about 350 images mostly from the oldest negatives that are beginning to curl and will start to lose color and tint soon as they are over 50 years old. I transposed about 200 slides out of 750, with close to 3,000 left. The slides are slower to process as the holder only takes 3 at a time. A little experimentation would help to guide you as to proper placement of the media in the holder to get the image right side up and not reversed.
I've got tons of 35mm negatives and slides so I'm in the market for a good film-to-digital converter. I'm looking at Wolverine 8MP, 14MP and 20MP. The 14MP and 20MP seem to be on back order everywhere, so I'm assuming they are pretty popular. Also looking at ION OMNI SCAN and PS9700. Any opinions or recommendations?