I have owned both and I much prefer the 'X'.

I look at it this way (and I think this idea was touched upon in an earlier response, but bears repeating):

You can probably do anything with the Plain Blade that you could with the Serrated Sheepsfoot. There certainly may be circumstances where the Serrated Sheepsfoot may be a bit better suited to the task, but there's probably not going to be a situation in which you need to cut something and the Serrated Sheepsfoot would do it and the Plain Blade just WOULDN'T!

On the other hand there are a great many things you can do with a File that you can't do with ANY other tool.

That being said, no Multi-Tool will cover all the bases for EVERY situation, so you need to decide what will work best for you.

-John