Have had great luck with the Magnaflow Hi-flow Metallic spun converters. The ceramic ones seem to fail on me more than I like, went Metallic and were still rolling down the road. Found this list of advantages one gets with a metallic coated converter.

There are two types of carrier/honeycomb/matrix available; ceramic and metallic. Metallic cats are the newer technology with many benefits including:
- Shorter light off time
- Less risk of overheating
- Less back pressure
- Larger effective area
- Greater catalytic capacity
- Smaller and more flexible design
- Thinner walls
- Higher mechanical strength
- Better resistance to thermal shock
Unfortunately the metallic carrier is much more expensive than the established ceramic technology.