There's pros and cons to each coin.
Main disadvantages of Grin:
The chain is "interactive", meaning both parties have to be online for a transaction to occur. Sort of like the lightning network, both channels have to be open. You can't just give someone your address or QR code and have them send you money whenever they want. You both have to be online for the transaction to happen. Compare this to zk-SNARKs, which literally stands for Zero-Knowledge Succinct Non-interactive Argument of Knowledge - meaning funds can be sent to an address whenever.
Grin is inflationary, there's 1 grin printed every second forever, meaning the annual inflation rate of grin won't come down to a reasonable level (say 2% per year) for a very long time.
The main advantage of Grin is that it is extremely lightweight, which is great for decentraliation. The typical Pirate Chain transaction is ~10X larger than the typical bitcoin transaction. With Grin, the typical transaction is roughly half the size of a typical bitcoin transaction.I love that it’s lightweight but I hate that both parties have to be online for a transaction to occur. That’s not convient at al.
If you want to use the Grin tech, you can already do so in litecoin with MWEB. So Grin basically lives on in spirit with litecoin.