We are currently shopping for our third pool bot. Our first was a Dolphin DX3, our most recent a Polaris P825. The differences between the two are remarkable; both have their respective strengths. That being said, I am undecided as to whether we will try another manufacturer or return to Maytronics or Polaris.
The Dolphin's strengths:
- fine (sub-micron?) corrugated filters pull everything out the bot manages to suck up
- 60' cord allowed it to reach the entire pool (freeform, 28K gal.)
- accessibility of customer service; spoke with a product manager who encouraged me to leave it the bot water (provided we maintained healthy water)
- 5400+ duty hours before giving up the ghost
The Dolphin's weaknesses:
- Heavy
- Smaller filter capacity, requiring more frequent cleaning (and more prone to debris clogging the intake)
- PITA to clean (you'll be in the 'splash zone')
- Didn't climb well (note: the DX3 was billed as climbing walls, but not to the waterline, so it performed w/in expectations)
The P825 strengths:
- Climbed like Dean Potter (at least until it died - again, like Dean Potter) - would have straight escaped the pool if not tethered like a wild horse
- No problem climbing 90 degree benches and stairs (we named it 'Gnarls' for its proclivity to jump off benches)
- Transparent canister lid allows for easy checking of debris without removing the bot
- Filter canister is a breeze to remove and clean (vs. the 15 min. process to clean the DX3)
- Light as a feather compared to the DX3, thus easier to extract
- Points for the active scrubbing brushes, which kept the tile at/above the water line the cleanest it had ever been
P825 weaknesses:
- Finer particulates pass through mesh filter
- Weight loss comes at the expense of durability (the handle is a weak link in the design)
- 50' cord kept it from reaching end of deepest bowl, requiring brushing 1-2x per week
- Not as robust (approx. 30% of duty hours before dying)
- Having to deal with Leslie's (in our experience untrustworthy, and have a stranglehold on parts that often cost almost as much as the bot)
While our experience is limited to these two bots, the delta between their respective strength and weaknesses kind of surprised me. Though I guess the same could be said for other areas of home robotics (e.g., robot vacs) as well, so maybe it shouldn't have.
However, the most telling thing in our experience is that after owning these two, we aren't exactly rushing back to replace either of them. If I thought I could get the same use out of the Polaris as I did the DX3, I would likely go back to the Polaris, even though it required more active pool maintenance on my part (the brushing only takes a couple minutes to cover the area the bot could not). However, I am spoiled enough on the P825's waterline/tile scrubbing prowess that I am not inclined to return to the DX, either.
In the end, I don't think there is a one-size-fits-all perfect bot; the choice will largely be dependent on your needs, preferences, and requirements.
If you are willing to pull the bot after each use, despite my hang-ups with Leslie's and the bot's shortcomings, I would probably recommend the P825. But if durability/longevity are primary concerns, I would consider similarly-priced Maytronics offerings as well (CC Plus, maybe?).
Here is a great thread on robot cleaners however it is very lengthy 
