Your phone is basically a pocket-sized computer. It stores bank accounts, credit cards, passwords, and maybe some embarrassing photos. And where there's personal data, you'll find hackers and malware designed steal it. This unsuprising trend is still in the beginning stages, but be smart and get ahead of it.
Each offers the basic malware and virus detection software, but there are a few differences. For example only Lookout allows you to back up your data, but Avast has several options to protect your data if you phone is lost or stolen.
I went with the Avast option for that reason, but take a look at Cha’s comprehensive reviews and choose for yourself.