I believe that Nokia has the best chance of turning around its company. For me, RIM is on the way out. Businesses in corporate America are also starting to ditch RIM for other phones. Nokia wasn't so heavily reliant on businesses and that's where its strength lies in regards to a turnaround.
I believe the turnaround prospects are better for Nokia. Nokia is better known and many people have some type of experience with the brand. I think hope for RIM should be abandoned. Out of these two, Nokia is the only one that has a real chance of taking its market share back.
The turnaround prospects are better for Nokia than RIM, because RIM only had one product, and it was trumped. I don't know of anyone who has a blackberry anymore. But Nokia still makes some good cameras, and they can rebound with a variety of different products. They are more likely to be successful than RIM.
Nokia continues to put out new and improved phones (shop at any phone store to see) and is attempting to compete in the marketplace. RIM has Blackberry, with its name recognition, but isn't doing anything new and exciting and is counting on that name recognition to carry them out of the mess they are in.