What's the current recommendation of file system?
ext4, btrfs, ZFS?
Is there one better suited for a laptop/desktop and a server?
Is one better for RAID?
Is one better for speed?
Is one better for resiliency?
It's possibly better for performance, depending on use case. If you're dealing with easily compressible data, then you can enable compression, which can speed up your reads/writes since you're reading or writing less data. You shouldn't get a performance hit on non-compressible data, since it will adjust its compression when it gets non-compressible data.
I really like ZFS, and it's definitely more robust than most other filesystems, but there are multiple solutions "if you care about your data".
in the begining of 2019 this page had a big fat warning:
The parity RAID code has '''multiple serious data-loss bugs''' in it. It should '''not''' be used for anything other than testing purposes.
Someone watered it down in march, but it still doesn't look much better.
The presentation "ZFS: The Last Word in File Systems" from its debut in 2008 is a good introduction. Part 1 (of 3) probably best explains how different it is from just about anything else out there (even now, in 2019):
Part 2 show some extra niceties / features, and Part 3 is a demo and Q&A. Watching Part 1 at least is worth it for anyone curious; 2 and 3 are optional.
Not all databases do buffering: Postgresql does not, and is generally built around an OS's normal I/O buffering.
2017 sub-thread on this topic:
$ curl -s http://us.cdimage.ubuntu.com/ubuntu/daily-live/current/eoan-desktop-amd64.manifest | grep 'ubiquity\s'
If you don't know what ZFS is you're probably better sticking with the default (EXT4).
ZFS supports send and receive, meaning a volume can be sent to another ZFS pool for backup.
Compression can save on disk space, and in some workloads be a performance benefit trading CPU cycles for IO savings, but this is probably more beneficial on data volumes compared to system volumes.
All of the above will be dependent on any limitations present in the options the installer provides, which apparently will be expanded in the forthcoming 20.04 release.
Now that it's fully integrated into the installer, you'd have to have a really good reason not to use it. It's just so much better and battle tested than any of the alternatives.