Reputation of university versus quality of work for research assistantship
All other things being equal I'd take the Germany option. Reasons:


You can't be sure if you want to do research yet. I know you said you do, but if your undergraduate was anything like mine then this thesis work is your first real contact with research. Research is nothing like coursework, and it's possible you decide afterwards that you don't actually want to do a Masters / PhD. I would therefore try to hedge a little, and in my experience with job searches, the institute's brand name is more significant a factor than the identity of your supervisor or the topic of your thesis (this assumes you'll complete regardless). Exception: if it's likely you'll work in India and the Indian professor is well-known in the country, then consider staying.
You can't be sure which project is more interesting. Yes, you can say that the ultimate aim of one project is more interesting than the other, but the actual research work is different. For example you might start the project and then find that the best way to proceed is to make your code more efficient. If you dislike figuring out how to vectorize code, then the ultimate aim matters less than the fact that you still have to do something you dislike to get there. Taken together with #1, this means I would not place much importance on first impressions of which project is more interesting.
Exposure. Assuming you did your undergraduate studies in India, then going to a different country gives you experience you cannot get by staying. You'll see a different culture, different way of life, different people, different currency, and so on. This can't be quantified, but it's valuable.
Networking. You will reach a different group of machine learning specialists by going to Germany. The wider your personal network is, the better.


Other things to think about:


Timezone. Going to Germany puts you in a very different timezone from India. You'll also be able to visit home less often. Will you still be able to socialize with your friends / family / significant other? 
Finances. Germany is more expensive than India. Can you afford it?
Personal happiness. Will you be happy in Germany? For example my mother, if she went to India, would probably be eating at McDonald's every day because she can't stand Indian food. If something similar may happen to you - stay in India.