Better content by a mile if you're in some of the good ones. Speeds are always good on private trackers but public trackers can have good speeds on popular things too.

Some stats (I edited the name into each one so it would be easier to differentiate):

• RED (1st largest music)
• OPS (2nd largest music)
• BTN (Television)
• PTP (Movies)
• HDB (All HD content)
• GGn (Video games)

Better privacy is objectively true but it's only security by obscurity, so it's ~99.9% bulletproof. You can generally torrent without a VPN on private trackers, though some of the larger "semi-private" mega trackers like IPT/TL/etc may still have a tiny chance of getting ISP letters. For a copyright holder to serve your ISP a letter they need to be in your swarm with you. Private trackers are difficult to get access to and have much smaller swarms than public trackers, so copyright holders usually don't bother. The easier a community is to get access to, and the more users that are hanging around in swarms, the more appetizing it might be for them.

Edit: Retention is also really good on private trackers. Most people seed everything forever on private trackers, so you don't have to worry about content being "fresh" for it to be available and seeded.