I’m going to start by mentioning Apple discourages all of the above and prefers you make a free app with in app purchases. Having said that, here’s what I think happens depending on which type you use.

Using “Lite” for the free version of “Pro” for the paid version (or doing both) makes the user more likely to get the free version. After all, they’re not a professional, especially when “Pro” is applied to mean ad-less. Who in their right mind needs the “Professional” FML reader? When people hear “Pro” they’re probably going to think of desktop Photoshop, and if they don’t use that then they don’t need your “pro” app either. I’m guessing using “Pro” and “Light” are somewhat effective.

“Free” is probably the most effective simply because it makes the user feel cheap each and every time they see your app on the home screen. If they use your app long enough, their internal embarrassment might make them upgrade at some point.

“Express” is probably the worst name you could use for your free version. Express means fast. To a user that probably would’ve bought the paid version, express can mean “without bloat” or “better startup times”. If I use the express version and never know what features I’m missing I’ll be happy as a clam. So with that in mind, Express is a great idea for the name of your $0.99 app when you also sell a $4.99 or $9.99 app. You’re getting a customer, and you might get a double customer. I wouldn’t attempt applying this to games.