I use the free version of Pcloud for several months now. So far I don't have much issues with it. Speaking of security, they claim on their website that they are really safe and that you always can try to break into their servers, but they say that till now nobody was able to do it. Probably this is also a little bit of an advertisement talk, but it seems quite safe from my perspective.
You can get 10 gb for free and if you install the desktop client, which is neat and light, you get 1gb extra. There was also a promotion in a
thread here on the forum that you can get 50 gb for free, but that one has expired.
They have a mobile client too, which is quite simple and easy to use, but I have seen better ones.
The download and upload speeds are also very good (but depends of course on the quality of your internet connection).
One other good thing about this cloud provider is that you can view your files on their website. If you log in with your browser (and also the mobile app) you can listen to your music and watch videos in their player and view pdf and other files directly in your browser, without the need to download them first. That is something not every cloud service offers (the less known ones for example).
Overall a good service and 10 gb of free space is always welcome. It's a service that is slighty becoming more popular. Sure worth a try.