I have always been partial to wearing sporty watches on bracelets, but the blue rubber strap on the Plastiki is a winner and looks great, too.
When I bought the first Aquatimer Cousteau a number of years ago, I found the rubber strap to be hot and uncomfortable. I put the watch on a bracelet and loved it. I never wanted to try another IWC rubber strap after that.
Alan Ross was nice enought to let me try on his new Plastiki at the Phildelphia gathering. The rubber strap looked and felt great! I don't know what IWC changed in the composition of the rubber, but it worked!
So in answer to your question, both look great. I would be tempted to buy both and change from time to time. I'd leave the black rubber strap for a different watch.