Having done quite a lot of internships myself, and tried multiple types of companies and teams, I would definitely recommend you to try finding an internship in a small size company, where you'll be challenged on multiple skills, and have less risk to be used as a disposable asset.
The best internships I did were in young startups, where you can and have to be as independent as you can.
The tech stack you should go for is your decision only, I don't see the point of choosing something you dislike ! Though, if you don't know where to start, web-development is the most easy kind of internship to find (and always good to have a try if you don't know about it), or Java development is also pretty common for interns.
In any case, assure yourself that the company hiring you for an internship states a clear goal for you during your time there, with some milestones for example. Lastly, try to get in touch and build a strong relationship with an internship referent. Having a mentor in a company is important, it is even more as an intern.
Hope that helps !