I guess I look at all of the main ones -- 1% rule, ARV, projected cash flow, etc.
A deal is a deal when multiple projections prove profitable. I tell myself this all the time -- if it's a mediocre deal in a perfect world, and a horrid deal if things go south, then I leave it to some other investor who has a higher risk tolerance.
Ultimately, some folks do great with those -- maybe they do their own work, don't have a day job, manage themselves, and are rockstars at all of those things, allowing them to accumulate volume and properties. That's not me.
Ultimately, YOU have to decide what's within your goals and risk tolerance. One area I invest in within NJ, the 1% rule doesn't work...it has to be closer to 2% because of taxes and the age of the homes. But maybe in Philadelphia, investors are fine with 0.5 to 0.8%, and are banking on appreciation...none of us are wrong...some of us might be stupid, but not wrong.
Whatever you decide, you have to be comfortable and happy with. Information is key and the more information you can glean, even at a cursory level in your area, is going to make you smarter and you'll make better decisions.