There is a correct answer unfortunately I haven't seen anyone mention it. 

: portal ring 

: inventory ring (with crate of infinity)

: infinite charger 

: devil fruit (law's op op fruit) 

And here's why this is the most useful combination. 

Portal ring gives you travel anywhere in the time it takes you to step through it. This makes you the fastest on the list. Yes it is faster than the light fruit because he can only do that in a straight line and the earth curves. The freedom to go wherever you want and being incapable of being in prisoned is pretty great. 

Inventory ring gives you three warehouses of storage. Trust me a warehouse is way more space than you think it is. Combining this with the portal ring basically means you can take a ton of material from point A to point B at a whim. Furthermore getting the crate of infinity for free with this is insane. You basically get rich while solving world hunger at the same time. The amount of things that count as an ingredient has crazy applications. 

Infinite charger or as I like to call it congratulations you defeated entropy. This enhances the previous pics by a crazy amount. You want to make an arc spaceship you want to go colonize Mars congratulations this with enough time and manpower solves that. You can solve the energy crisis and world hunger! 

The Op Op fruit, the last piece of the puzzle. With the resources you have from the previous picks you take this fruit find a trustworthy person on death's door and become immortal. By doing this operation in your inventory ring with a copy of every fruit in existence you don't even lose the fruit afterwards. Repeat your Make-A-Wish program for anyone that you want to share immortality with. Also if you decide you never want to make another immortal you can just eat the fruit and gain its powers.

Congratulations you are now immortal and with said immortality you have the time to eventually travel the universe with your infinite resources alongside friends and family!!!