Ole Nydahi and Trungpa rinpoche

[underthetree]

Your main concern should be whether the group you choose is going to deliver authentic dharma teachings to you as their main and indeed only priority. I don't know very much about either of these two organizations but it's plain that a good deal of their energies go into maintaining their distinct identities. They are brands in the modern sense (unlike Drikung vs Drukpa Kagyu, for instance, or Sakya vs Nyingma) and at least some of your interaction with them will involve identity politics of some kind - as is proved by the fact that you've (sensibly) asked this question before joining either group.

This is my personal opinion so it's worth nothing at all, but I believe that one interaction with a great teacher will set you up better than decades of attendance at a run of the mill centre.

[martin123]

Both Trungpa Rinpoche
and Ole Nydahl thought that Tibetan Buddhism needs to be adapted to be
accessible in the West. Both changed it in their own ways, Other Kagyu
teachers have been more conservative. There's a nasty argument in the
Karma Kagyu over who is the real Karmapa. Ole Nydahl sided with one
claimant and Trungpa Rinpoche's organization eventually sided with the
other, though it stayed neutral in the controversy for a good
bit.

I wouldn't like to think that i would have to side with one group or another due to political pressure

[Yudron]

Both Trungpa Rinpoche
and Ole Nydahl thought that Tibetan Buddhism needs to be adapted to be
accessible in the West. Both changed it in their own ways, Other Kagyu
teachers have been more conservative. There's a nasty argument in the
Karma Kagyu over who is the real Karmapa. Ole Nydahl sided with one
claimant and Trungpa Rinpoche's organization eventually sided with the
other, though it stayed neutral in the controversy for a good
bit.

I wouldn't like to think that i would have to side with one group or another due to political pressure

Martin, if you are a beginner in the Dharma I wold suggest going to every Dharma center near you and seeing how much you enjoy going there, and take classes in basic Dharma. There is no commitment there. I did so at Shambhala Centers, and it was very valuable. Start practicing regularly. In so doing, you will develop your qualities as a student, and become a good vessel to receive more and more profound teachings. But,eventually, in order to be a Vajrayana student, you will need a serious commitment to an excellent lama that is not only highly qualified, but with whom you feel a personal connection. Faith and devotion are big words, but--at minimum--you will need to trust your lama a lot and feel a connection to him or her. It is best to see him or her at least once a year in person. In addition to that it is important to have access to people who can answer the raft of questions you will have constantly at first about details--such as a senior student or lama affiliated with your guru, either by phone or email or in person, during the interval between visits with your guru (assuming he or she travels extensively.) Famous lamas are not necessarily better than lesser known lamas.

The main lama for the Shambhala center is the Sakyong, who is a qualified guru. Trungpa Rinpoche has been gone along time. The Sakyong is who you would eventually want to meet and evaluate, it doesn't really matter that Trungpa Rinpoche thought about some other lama long ago. I'm not sure about Nyedahl's center, but I think the Karmapa he is affiliated with is the guru there... you would want to meet and evaluate him and Mr. Nyedahl, not the 16th Karmapa or some other long-gone guru. But, don't stop there, over time meet a lot of lamas and pray that you meet your guru or gurus and it will be obvious when you do.