As all tradeoffs it depends on your requirements. lz4 is ridiculously fast so it essentially gets you more ram for free, zstd is a lot more CPU-intensive but also has a much higher compression ratio. So if your RAM is severely undersized for some of your workloads and / or you're not especially CPU-bound until disk swap takes you out, then zstd gives you a lot more headroom.
As all tradeoffs it depends on your requirements. lz4 is ridiculously fast so it essentially gets you more ram for free, zstd is a lot more CPU-intensive but also has a much higher compression ratio. So if your RAM is severely undersized for some of your workloads and / or you're not especially CPU-bound until disk swap takes you out, then zstd gives you a lot more headroom.