What do you consider a great long-term investment?

Hello everyone,

I'm beginning to invest again, albeit more responsibly now. I was investing tons during the initial months of the pandemic and saw some very nice gains, also very big losses. Though, luckily for me, I made a lot of it back with a nice profit as well. I took a break from investing to sort of plan out my method of investing and I've sort of accepted that long-term is my goal. For starters, I've chosen to use fidelity as my main brokerage due to the sweet low to non-existent fees. I figured that I'd invest the majority of my funds using fidelity, and my play money into Robinhood. Though, I'm curious as to what your portfolios consist of at least for the long-term context. I've looked at VTI and I'm eager to invest there, though, what do you all suggest? Also, where can you direct me so that I can do more research on the individual stocks and ETFs? Any good websites or forums?

Thanks.