Well, I never finished the side by side comparison so here goes.
Winner: Betta 2
While both will skim the surface of your pool the edge goes to Betta primarily due to battery life.
Battery Life: Betta by a landslide. The Betta will run all day and night for most of the year. As long as your pool gets good sun during the day. This time of year, and probably through to January it stops sometime in the night and will start up again around 9am. The Ariel has about 3 hours of battery life after a full charge.
Basket Size: Betta by a hair. The Betta does have a bigger baskets but the Ariel is not small by any means. This probably not a deciding factor unless you have an enormous amount of debris that falls in your pool (some members here do). Also the Betta mesh is plastic while the Ariel uses steel (the steel has just a touch of rust).
Maneuvering: Betta by a hair. Both steer to avoid obstacles but the Betta seems to do it a little better. If your pool has a lot of corners this will make a difference, in a free form pool not so much.
Stuck on steps: Ariel by a hair. The Betta rides lower in the back and requires my pool to be at the highest level. It has pegs to help it not get stuck but they are more of pain to use. There is some real room for improvement here and I know some members have modified their legs.
Longevity: Tie. They both break. I have had to send my Ariel back a few times (their service is pretty good with shipping a new one and returning the old). Although my Betta has not broken down yet, many other members have.
Warranty: Betta by a year. You can negotiate a 2 year warranty with the Ariel, but you can buy a 3 year warranty with the Betta 2. Based on the longevity comment above you want the longest warranty you can possible get. You will use it. I also recommend using a credit card that will extend the warranty with any of these purchases.
Noise: Personal preference. The Betta is quieter, it uses propellers and the Ariel uses paddles. The paddles make a splashing sound, it’s not unpleasant but it is there. It depends on whether you like noise coming from you pool or not. Also as the Betta starts to fail, its motors start making more noise.
Power: Advantage Ariel. The paddles on the Ariel drive more power. It is less affected by the wind. It is also rare but the Betta will occasionally get stuck in my skimmers when the water is lower. The Ariel does have enough power to dislodge itself or just not get stuck at all.