Hi Monique,
I have a plaster pool and only have personal experience with the Dolphin M500. The reason I suggested that aggressiveness could be something to consider is because I read it in a thread here when I was shopping robots. Unfortunately, I do not remember the thread that I saw that discussion in. But, as I recall, the poster was replacing an older model robot that had been rough on their vinyl. The brushes on the all the Dolphins I've seen in person are softer than they look in pictures. But, perhaps the poster was referring to the suction power being too strong for the liner. I believe that the poster who was talking about this ended up with a Dolphin S300 and said that it was working better for their vinyl pool.
I remember that post because I was looking for the most aggressive I could get!
It probably would not hurt to consult a dealer or even a vinyl installer about which models are best for any particular liner and of course check with people here at TFP who have vinyl pools and use robots. A robot is a big decision!
Hope that helps!
Crystal