I always tell people to go with the ATR if they are ever going to hit terrain at all. Plus, all round it is just a tougher product.
I personally ride the TimeBomb, but I have taken quite a few sets on the Viva ATR shape. I really like the Viva and would say it is better for a beginner for the following reasons.
1.) It does not have a variable edge. There is a lot of hype around boards with soft edges in the bellies. They give you more edge to edge forgiveness, but simply don't handle chop as well. For a beginner the snaky feel of a soft-edged board can be tough to manage when you really need consistent approaches to the wake.
2.) The Viva is a faster board. The One is much faster than previous year's shapes, but it is still not a fast board. On your approach to the wake if you come off the gas you are going to lose speed fast. When I see beginners on slower boards flattening off before the wake is the most common problem.
All that said, I ride the Timebomb and love it because it is very aggressive up the wake and very forgiving on the landings. They are both great boards for different reasons, but my advice is the Viva for you.