2.53.0 is a full release with LTS. Once 2.53.1 is done, it will replace 2.53.0. both of these are primarily bugfixes to 2.50.x with some minor improvements.
2.55 is the active version with gigantic upgrades.
Feel free to read the changelogs:
2.53.1 Changelog
2.55 Changelog
There is no reason not to use 2.53.1 at present, as even in a Beta state is is far more stable than prior versions and it fixes many bugs.
If you want new features, use 2.55.
There will always be two active versions while I am in charge: The most current active and stable version, and the 'next version; in development. That said, 2.55 is generally stable, too, even as an Alpha build. We now use proper Semver.org version semantics, so Alpha now is Beta back in 2004-6.
In general, there will always be one 'Release' version, one Beta or Gamma version, and one ;alpha or beta' version. Development is more active now than it was in the past, and we work on more than one version simultaneously.