This question gets asked all the time, and it's about to get more complicated. I'll cut to the end and then explain in more detail -- it's both!
Energi Cryptocurrency is a coin that is based on Ethereum - meaning Solidity smart contracts written for Ethereum can be ported directly to Energi. There are a lot of other important differences such as the staking rewards (Energi has been PoS since this spring, while ETH has a lot of work still to get there), and the EBI (Energi Defense Bureau, which helps keep the community safe from scammers). There's more, but suffice to say, the Energi coin has a lot of features that you can only get when you're running on your own blockchain.

So what's this about a token then?
Just this week, Energi launched the synthetic token NRGE. This ERC-20 token lets trader hold and trade Energi while staying on the Ethereum blockchain. Like many other synthetic assets, there is NRG locked up on the native Energi blockchain to fully back the NRGT tokens. In fact, they can be exchanged back and forth (see the Medium article for more details).
If you're paying attention to the DeFi world, this is the cornerstone of making an asset useful in the DeFi world. So now, not only can you acquire Energi without using any centralized exchange, you can also use Energi in Defi!
Safety first!
Ok, if you use Uniswap enough you have probably seen the warnings to verify that you're using the correct address. It's always possible for impostor tokens to spring up, or for there simply to be a name collision. The contract address is what identifies a token uniquely!
The contract for NRGE is 0x1416946162b1c2c871a73b07e932d2fb6c932069. So, to trade you can either put that address into Uniswap or you can go directly to the NRGE swap page
Save on Gas!
Also a quick tip - check the current gas fees on Etherscan's gas tracker. Gas price fluctuate during the day, often by a factor of 4-5. Watching gas fees can make transactions much cheaper for you.

What's the difference?
For me, one primary difference is the ability to "stake" your NRG coins. This makes it advantageous to hold NRG as a coin on the Energi blockchain.
However, the ability to trade on the ETH network and use NRG in DeFi is pretty awesome. In the end it depends on how you need to use NRG that will determine how you want to hold it.