Allow me to be a little more specific. With MEGA, you have a Master Key that you have to download and hold onto. If you lose this key and you forget your password, you are 100% SCREWED. The key in and of itself poses a security hazard if you plan on sharing anything through your MEGA cloud service for one simple reason. You need the key in order to be able to view any content, which is the same key that is used to recover your account and reset your password, and therefore, anyone whom may have their hands on a copy of a shared file link potentially has access to ALL your files, because as I said, this master key is required to view anything in your account. In the event that your key should ever come to be in the wrong hands, there is a grave potential for your account to be compromised, as it is the key that ultimately unlocks everything for you and allows you to change your account password.
So... MEGA advertises this as a good thing, when in fact, the whole concept of it all unto itself poses a security hole that MEGA refuses to admit. In fact, when I questioned them on this very point, every time they changed the subject on me and refused to answer my question. This tells me that they know damn well that this security flaw exists, and that they have absolutely NO intention of fixing it. So, with this I say, use MEGA at your own risk. From my experience, MEGA customer service is relatively ok, as long as you do not ask the right questions with regards to their security, and as long as you do not comment on how expensive their prices are for their paid platforms.
Now, as for Dropbox, that brings up a whole other realm of security flaws. If you're going to use Dropbox, the first thing that you need to know is that their customer support is TERRIBLE. More often than not, they'll send cookie cutter emails, which have absolutely NOTHING to do with what you've asked about, and when you do actually get a reply that isn't a cookie cutter reply, it's generally rather dismissive. I know this from first hand experience. It's been well over 6 months now that I've been complaining about a bug within Dropbox if you're using Ubuntu 16.04 in Gnome. Every time, I just get the same response about how they're looking into it, and they have no estimated time of resolution for the bug, yet they keep cranking out new features, catering to other platforms, while completely ignoring that their Linux app isn't what it should be. Also, if you're using their mobile app, be prepared for connection issues with your internet. The second you try to upload a mass amount of data, such as your entire pictures collection on your phone, or even worse, a long video, be prepared for the Dropbox Mobile app to suck back ALL available bandwidth, rendering your entire internet connection 100% USELESS, especially if you have a slower upload speed.
Aside from the downright TERRIBLE and utterly INCOMPETENT customer service, the second problem that you face with Dropbox is that all their data centres where your information is stored are located within the United States. This means that you can be damn sure that the US government is looking at your information because within the US, privacy (especially online) is a myth. For this reason, I would strongly recommend that you make use of some sort of third party encryption to ensure that your information cannot be compromised. These services however are a paid service, sadly.
So yes... Because of technical issues with the software, security holes that can be exploited, and absolutely TERRIBLE customer service, I simply cannot recommend either one of these two. I would strongly recommend that you use any cloud service other than Dropbox, MEGA, or pCloud. Simply put, my issue with pCloud is that they spy through your files and decide what you are and are not allowed to have in your online storage. I was actually banned from pCloud because I had an adult photo shoot of myself contained within my files, which they objected to. So... Be very careful with these services.
I've been looking at an alternative service such as Degoo
, but sadly, because I am not a Windows user, I cannot take advantage of what they have to offer.