About asterisk releases

What’s the most stable version of asterisk??
What version work better?

the most stable are the current relases of 1.2 (currently 1.2.30) and 1.4 (currently 1.4.22)

1.4 and 1.2 both work equally well but 1.4 has more features than 1.2. For a new install I would just go with 1.4 as 1.2 has been in security fix only release mode for nearly a year now (no new features and no bug fixes not security related). With 1.4 they still backport small new features and many bug fixes as well as fix bugs that only effect 1.4.

1.6 was just realeased this month, if your install is small or you are just in the initial testing phase and dont plan a full scale rollout for another 4-6 months you may want to start on 1.6. If you need something stable immediatly definately go with 1.4 and wait 4-6 months for 1.6 to stabilize.