Depends on distances, frequency of usage, and parking costs.
I was checking on our local car rental rates, and it looks like the most basic option for one week is $225 (with tax included) and renting a minivan (Dodge Grand Caravan or similar) for a week is $400, $472 with tax.

Plus fuel costs, of course…
I’m about three days into the experiment and I believe I’ve spent $70 (over 6-7 different orders depending on how you count) on Uber, with at least one round trip ahead of me. I may even finish up under $100 for the week. In fact, I suspect I will.
Obviously, I’d get more use and flexibility out of a car rental, and maybe I could get a better deal than the numbers I found (the prices I used were from the first company I saw), but it’s not clearly the case that a car rental would be the cheaper option. I would need to average $32 of Uber every day for a week to reach the break even point–which I’m not going to do.
So, again, why do we think of the Uber as being the luxury option while the car rental is the sensible, economy choice?