Chain length - geared

Guys, sorry to bring this back, but I'm at confused.com. I found three different ways to measure the chain and all of them say it's the best way.

1. Small-Small and make sure chain is not touching rear derailleur
   
2. Big-Big +2 links (measuring without derailleur)
   
3. Big ring - small cog - derailleur's jockey wheels vertically lined up.