Pressure side vs robot - is that the real question? Obviously, the pressure side needs plumbing and a pump, so if for an existing pool that doesn’t have the plumbing, it’s a moot point.
I’ve never had a robot, but have a Polaris pressure side cleaner - don’t recall the model, a 380 maybe? It’s 18 years old and still works like new. I’ve never had to replace a single part on it. I have had to repair the hose and replace the valve thing that makes it float up every 5 minutes or so. I’ve also had to replace the pump once. I love the size of the large debris bag. I leave it in the pool 24x7 unless we’re having guests. It’s super easy to remove - just disconnect it from the side port and pull it out. While it picks up pretty fine debris, it doesn’t do so as well as a robot, based I what I’ve read here. But it cleans my pool quite well. I wish it would do a better job of covering every inch, but the path is pretty random.
From what I’ve read, robots clean extremely well, but longevity is an issue, especially for the price. Most say that they are to be removed and stored instead of leaving in the pool. That’s the probably the number 1 reason I’ve stuck with the side pressure. I want simplicity and having to lug the robot in and out of storage would be a pain, especially if stored in my garage. That would mean lugging it from the front of the house, around the side and to the back. Even if on a cart, it’s a non-starter for me. I have a shed in the back that would be a little more convenient, but it’s small and pretty full, so I’d need to make room. I like being able to press a button to start the cleaner or program a schedule - don’t even have to walk outside. Also, when I evaluated several years ago, the robot debris containers were pretty small. I have lots of trees and storms can knock enough leaves down to cover the bottom of my pool, so the small debris container was an issue, too. Capacity may be better now. The need to run an extension cord for power was also a bit of an annoyance.
I went through the decision process when replacing the cleaner pump. After researching, it was an easy decision for me - stick with the pressure side cleaner.