If you’re interested in lockscreen apps, your two best options are S'more and ScreenLift. These are the most popular and reputable lockscreen apps and are the most likely to issue timely payments when you cash out.
If you're looking for other ways to make money, It's also worth looking into survey sites like Swagbucks and Survey Junkie.
To be sure, these sites take a little more effort than unlocking your phone. But they offer plenty of paid opportunities to participate in market research studies, and you should be able to make a little more money than you can with lockscreen apps.