I would be pro car rental. It gives you a lot more flexibility and like mentioned above if you plan on doing taxis it will be a lot cheaper in the long run to rent a car.
It would give you the flexibility to go downtown, out to Hoover Dam, or to go off strip to eat, or to a locals casino some where in the valley.
You might look at renting a car for the first day or two to see if you like it and then return the car if you find it is not doing you any good. You are in a good central location on the strip and maybe you would want to just walk around that area for day or two without a car. Five days might be a bit much to just stay on the strip and the car would give you the freedom to get out and about.
Since you are staying at Paris I would get familiar with Koval Lane (it is behind/to the east of Paris hotel casino). I think the street that gets you to the self parking garage is Audrie (or something like that). You could look at a map online. If you use the self parking garage it is a simple walk down an escalator to the shops/dining area that is between Paris and Ballys. Once you hit the casino stay to your left and you will get the elevator doors. Or you can simply valet park near the check in area.