It can be a bit daunting trying to figure out how best to protect our devices and as you see, there are 1000s of options!
Your first line of defense is to simply not mess around with Android’s default security settings. Each and every phone and tablet comes with “Unknown sources” disabled in the security settings. If you want to downloaded from outside Google Play (like Amazon), all you need to do is check that box. Leaving this disabled keeps you safe from virtually all Android malware, because there’s *almost *none of it in the Google Play Store.
Android apps also exist that are “spyware” - I would say you don’t want them on your phone because they snoop through your information. These are easy to avoid by reading the permissions granted an app before installing it. If a free card playing app wants access to your contact list you may want to skip that download.
I suggest getting an antivirus app like AVG or Malwarebytes - free services that have been around for quite some time and can offer protection. I also usually recommend CCleaner as an assist to the antiVirus you choose. Though these are arguably not needed either because the Google Play Store does a great job of vetting the apps before they become available for you to download.
Battery Doctor can lead to battery savings, but it can also undermine the operation of your phone by killing processes that make it function most optimally. It gives you convenient control over brightness but you can do that manually if you really wanted to. Your phone may be slower because the battery saving app is trying to stop some background applications - which don’t want to stop.
Clean Master, CM Security and Power Clean… - I would get rid of them. Manual Cache clearing is of course good (and is really simple) but there is no need of a separate app for it. The idea behind apps that claim to boost your memory is to close these background apps systematically. Unfortunately, this exacerbates the problem. Memory and battery life is used to restart the apps, and this constant closing and restarting of apps can make your phone unstable.
And since I’ve taken too long as it is - I would warn about click bait. Don’t fall for it. If you get a pop-up on your phone while reading some article or visiting some website that says your phone is infected and just click here, blah blah blah - don’t fall for it. Just back out/go to the home screen and all should be good.