Hi,
I'm the author of BTM, the Bitronix transaction manager. As such, I consider myself biased and won't give you any advice on which implementation you should use.
What I can tell is is that I'm not working for Atomikos but rather working with them. Both products are still alive and kicking and are developed in parallel. You can safely assume that BTM will still be maintained in the long run and should not rule it out based on this argument.
Finally, I'd suggest you to stick with Spring and JTA as it will allow you to have a much better design and no vendor lock in as you could have by using OpenEJB's transactional capability.
Ludovic Orban
