I can't speak for or against Dropbox as I never accepted their pricing. I went with Copy by Barracuda and at first was quite happy. It was just like Dropbox but was significantly more generous with the amount of storage.
Then I got a notice that it would be dissolved, killed, ended. I had to make sure all those files were backed up. They then shut down the service.
And it seems every company kills their stuff eventually.
Twitter cancelled Vine. Twitter is ending Periscope. Google ended a whole boatload of online services over the last few years. Facebook makes random changes constantly and Instagram keeps adding features and changing their format. Now ads pop up, the order is random, and it's a bit messier than it once was. Plus, social media is at the whim of what the cool kids like, be it MySpace, followed by Facebook, twitter, instagram, Snapchat, etc.
I even quit SmugMug because they don't allow RAW storage under their normal pricing structure. Plus their prices got higher for commercial uses.
I gave up on the internet as far as trust is concerned. Now I use it to occasionally keep up with friends, send email, shop, read about photography, etc.
My current storage is my computer hard drive and a WD MyCloud. Two places. If one goes out I'll make another backup so that I still have my pics in two places.
I'm over all these companies that constantly alter perfectly good services. They simply cannot be trusted. And it's not because they are dishonest or unethical. They are trying to either stay relevant in a rapidly changing world or are trying to increase profit. But I don't want to participate anymore.