Not really an eDGe only question, you probably will get more respones in the Android section.
Dropbox and SugarSync really are more direct competitors and are considered "Storage" boxes. I have an account for each and each has their strength and bonuses.
But Evernote is really on a class of it's own, it's not really considered a "storgage" app, but more of an "Organizer" for folks on the go,
Evernote claim to fame is the ability for the user to take a picture, load a picture to their database server. At some point in time Evernote runs an OCR on the image and make that image searchable (you never see the OCR results). The idea is you can take pictures of your notes, schedule, recipes, or anything else you might have to recall at a later date.
You can also create text base notes or add additional notes to your images, upload documents. etc...
Then open up evernote and search for what ever you are trying to recall. The search is very fast and works great.
I do use it quite often for my kids sport scheduled, school schedules, business notes, etc. I've always stored images digitally since college so Evernote was something I really needed. The nice thing is I don't have to wade through images to get the one I need I can just do a search and evernote pulls it up.
Note on any storeage device make sure not to store sensitive materials even images because they can be scanned and archived. Evernote is upfront about this, but there is nothing stoppign dropbox,sugarsync from doing the same.