depends on the region and the brand name of the company in a particular region. Arthur D Little is famous for energy&utilities, oli&gas consulting. At Arthur D Little most probably you won't be staffed on international project at least if you enter in Germany or in Switzerland because:
1. at ADL every partner has its own P&L and they are not interested to send you abroad only if you have a unique expertise or they are really undestaffed
2. As a consultant in Germany or in Switzerland you are too expensive for other regions
Now in Germany ADl doesn't have many projects and all projects are mostly IT related.
Simon Kucher has excellent reputation in its area of expertise - Pricing. I heard from some consultants that they work on international Projects, even if their home office if Germany or Switzerland. I personally had very positive impression about people there.
In the end it depends on topics you are interested in and the region you will be working.