Use a Seam managed EntityManager - @In(create=true) EntityManager entityManager; (your option 2).
Thanks for your reply !
Do you advice Seam managed EntityManager because it's simpler ? more powerful ? both ?
Is it an advice for a newcomer (then for me ;-)) ? Or an advanced user (then for me in a few times ;-)) ?
It's one of the best reasons to use Seam :) It's harder to get LIEs.
Everyone should use it, there's no reason not to.