There are literally hundreds of thousands of active exploits and compromises floating around the Internet and a lot of them are targeted at the Android platform now that it's so prevalent. But no matter what kind of PR statements the anti-virus/anti-malware providers may make, there is no such thing as any one of them that's 100% effective. At best you should expect a maybe 70% level of actual protection. Plus you have to take into account while some exploits are specific to Android, most focus on our online services -- our phones get more exposure when we're interacting with online, but it's our data that's in our various online sites that are always exposed (we have to go on faith that whichever social media sites we use are keeping our accounts safely locked down).
So pick any A/V app you like, and it may or may not actually protect you, there are hundreds of variable involved. (Odds are you should stick with the more popular ones, they'll have more active development and support and that's really, really important because exploits and malware are always evolving and getting more sophisticated.) When you're so lackadaisical on how you use your phone when interacting with the Internet, A/V utilities can't protect you from yourself.