Many people forget that when you are hired into a position, there is generally a 90-day probation period where either the new employee or the organization can terminate the employment for any reason...this period is designed to address situations such as you have described where there is not a good fit between the organization and the new employee for any reason...this is the purpose of the period...you also need to remember that if you are still in orientation, that is a good time to actively make your decision...before you have used any more of the resources of the current organization...since you have a potential employer, you might consider discussing the viability of your getting the role and why you want to be in the employment in their organization, there is no need to badmouth the current organization, a simple statement something like, "I found that my career goals and their expectations for me did not align during orientation and do not think remaining with the organization would be productive for me or the organization." Good luck with whatever choice you make...