If it's only for park, then I would go with the thalls, it's a bit more narrow and park specific than arv.
But if you want to be able to take it through other terrain as well the arv is great!
In terms of flex, they are pretty much similar.
If you are into soft playful skis, the 2013 punx are amazing, and they are super light. Next years will be stiffer and have some rocker, but they are coming out with a new jib ski called the infamous, so you should check that out too. Ive had no issues with atomic durability for an entire season of riding.