It depends.
My parents are in Taiwan, where beetles are easier to obtain .
So when I was little, I try different stuff every year.
I started with local Allomyrina dichotoma and Dorcus titanus sika.
Soon after, I want to challenge some bigger species, including CCC, DHL, MA, DN.
DN wasn't successful (I think its the temperature, I had no clue that's a thing),
CCC were all short horns
DHL got to 120mm
MA got to 105mm
So I continued to breed the DHL and MA because they were more successful. both of them lasted 3 generation. I think because they were breeding with their siblings and caused a higher chance of death rate.
Then I started to pay more attention to stags and tried a few Dorcus titanus, Prospocolius, and Odontolabis species that are not native to Taiwan.
After I got to college, I went back to Taiwanese species again.
Then I started working, had to travel to Bangladesh, China, and now USA, tried breeding some local species in each country. there were about 2 years where I only collected the adults, because I know ill be moving again and wont be able to wait for the larvae to grow up and to emerge.
Anyways, now I have D. tityus, and L. elaphus.