The only PC apps I have used to download files, music and movies is BitTorrent and iTunes. I find BitTorrent to be more fast and secure. It protects your PC from malicious sites and viruses. I use the BitTorrent when downloading movies and files. I love the iTunes store equally. ITunes is simple to use and has many offers. I use it when downloading music files and and when organizing my PC.
Softpedia site has the free apps and they seem to have clean installers. They check for virus too. So they seem to be a good source for downloading the apps. Most of the apps there are free. And also some are the shareware app. I mostly stick with the free apps and that is good enough for me. I don't want paid apps due to financial issues.
Well, nowadays most YouTube videos are downloadable from the internet, so I just download them directly. In case I need an app I just get it from the Windows Store. However in case I need a third party app, I first watch a tutorial video on the internet, to verify that it works in the first place. In my mobile phone, I use google play store. Even though it has been lately hit by some black hats, I believe they will resolve the problem soon. Furthermore, I would still recommend, 1 Mobile Market for any one with an android device.
I use YouTube video-downloader app to download any video, movie, episode, or mp3/mp4 on YouTube -whereby I copy paste URLs of the clips I want to download to the apps for them to get downloaded in the quality-format of my choice and APK-pure software to download and upgrading most my PC's software. I'm impressed with both because they are fast, safe and much efficient than most I've come across.