Congatulations for getting at offer with Siemens Advanta!
This depends a lot on what you are looking for in the long run. Let's breakdown some criteria:
1) Specialisation: From my understanding, Siemens Advanta typically deals with technology consulting (software, hardware, AI, digital transformation, etc). Are you passionate about this field? If yes, this may be a great option! If you're not too excited about this and would like to explore different industries, then consider other firms too
2) Geography and Brand: Where do you want to stay? Is it Germany in the long run? Siemens is a very powerful brand in Germany, but outside of that MBBs have a much stronger brand than Siemens when it comes to consulting
3) Mobility and learning: MBBs and other consulting firms also give you more opportunity to travel for work, work across offices, and have stronger L&D opportunities
4) Work Life Balance: Its pretty clearly Siemens that takes this point :)
5) Culture: Are you looking for a more German culture or an international culture? This is very important for you to be happy. Siemens would not care much about MBAs and they respect engineers a lot more.
Hope this helps, happy to talk more on chat.
All the best!