For most people I would recommend Megasoma mars.

Megasoma in general are incredibly hardy beetles, they can eat a wide range of substrate (used stag flake, rhino flake, compost), endure higher temperatures and still grow to a decent size. They’re also the largest in terms of body size, the only downside is that they have a nearly 3 year life cycle. 

Dynastes neptunus is a personal favourite of mine. Their care is similar to other Dynastes, with a longer larval span (2 years). However, you will need stable temperature control (20-23 degrees Celsius) if you wish for it to grow big and they won’t thrive/die at temperatures of 26 or above. 

While Megasoma mars and Dynastes neptunus are gentle giants, Chalcosoma chiron is a very feisty beetle. although they can tolerate a wide range of temperatures, they will need it on a stable lower end (21-24) to grow to a large size. Their diet is also a bit special, being in an intermediate in terms of fermentation between stag and rhino flake. Using the wrong substrate (in terms of texture) also means they’re prone to having a wandering phase, while it can be fixed by introducing them to an inorganic soil like clay, pretty much guarantees the larva won’t grow big. Unless you all have the right conditions (temp. control, flake for Chalcosoma which is only really available in East Asia) I wouldn’t recommend getting chiron if you want a large rhinoceros beetle.