RAID5 tends to offer the fastest read and write performance, while maintaining a fairly strong raw to usable data percentage. Usually ranging from 85-90% raw to usable.
RAID6 offers great read and write performance, and depending on your RAID controller, buffering and settings performance can be close to RAID5. In some cases even beyond a RAID5. However raw to usable capacity is slightly lower ranging from 75%-85%.
RAID5 allows for a single drive to fail without any data loss. RAID6 allows for two drive failures without any data loss.
RAID5 rebuild times tend to be quite a bit faster, ranging from 50% to 200% faster, depending on capacity, RAID controller and the amount of data you have.
Neither is better or worse, but in generally RAID5 will give you a little more storage, performance and faster rebuilds and RAID6 will give you more data protection.
My personal favorite set up is a SSD based RAID6, it's maximizes performance, rebuild times and data protection.
