The hard plastic means it's not as easy to grip as silicone cases, or those with added grips, like Speck's Presidio Perfect-Clear with Grips case. Some prefer grippier cases for extra peace of mind.
Silicone phone cases offer durability, flexibility, and excellent grip. However, you'll notice that they can collect dirt, oils, and stains, making them look dingy or discolored really quickly.