@Jonathan Guerrero it depends on the quality of property you have and the tenants you are trying to attract in my opinion.
For the "higher end"/rent units I do the entire process through RentRedi. It's $19.95 a month and worth trialing because it has no contract or implementation like other software. Aside from screening it also has a lot of other neat features that will differentiate your property to people searching.
It gives the tenants a professional feel, and the screening is $35 once you approve an application. $35 is charged to them, and depending on how you are you can either credit off the first months rent or label that as your application fee. Your choice-I usually pass the charge them to make sure they are serious then credit it off the first months rent.
In the lower quality units I've found the "app" approach is proving to me more difficult than its worth. I send a PDF (not word or you will see prospective residents change wording) version of the lease. In the lease they provide you with their SS# and full legal name. We will then put the info in RentPrep and they get an email to approve or deny the screening request. You also have the option to pass the cost to the tenant or absorb it yourself.
I've gone cheaper in the past but the detail on both RentRedi and RentPrep is solid, and gives recommendations on other factors than just credit.
To mimic the other responses: I would also collect 2 paystubs, 1 W2, and a reference. Often I don't call the reference if everything else is stellar-but it says a lot about the prospective resident if they provide one vs. "available upon request"