It is a very personal choice and everybody has their preferred brand that they use and for different reasons.
I am a NSI lover, always have been and I can't see that changing in the near future at all.
I use Attraction L&P, Balance gels and Polish Pro and all the other products that go along with these systems and I have not had any problems with any of them.
Training is different for every country but the training I have had here in Australia with NSI was fantastic, couldn't fault them at all.
At the end of the day, they choice is up to you, have you tried sample packs from both companies to see which one you work with better?