I had a fiberglass pool with one skimmer and bought a Great White suction cleaner. The pool had a sand filter so it was a good combo since everything from a suction vac goes into the filter. I probably wouldn't pair a suction cleaner with a cartridge filter. Unless you just like cleaning the cartridges a lot. In any case, when the pump came on, the cleaner came on, it climbed the walls and did a good job.
We had our current pool built and builder put in a pressure line with aux pump. We have a Polaris 280. It works okay, picks up big debris, gets stuck occasionally. The hose even with the swivels gets tangled in a knot, especially before the water warms up well. The hose isn't as flexible when cold, something to consider in your area. You can get a silt bag which is a finer mesh bag for it but it really doesn't pick up dirt. I have had to rebuild mine already after 6 years. The wheels and plastic gears don't last long. You can swap some of the wheels around to get fresh gears when they get worn down but eventually have to rebuild them.
I just bought a Pentair Kreepy Krauly Prowler 820 based on a friends recommendation. He's had one for his pool for several years. Pretty inexpensive for a robot, I think it was around $650. I really like it, has two filter types, one is a mesh for when the pool has more junk, and a pleated one that will clean up fine silt. So I am a happy convert from both suction and pressure to a robot.
I agree with most of these recommendations. Get the suction line for your vac and get a robot.