As far as servers go, this would be fairly accurate summary of it:
Nostralius, buggy and laggy with ability delay during prime-times as their server cannot handle the playerbase. Numerous crashes and forums oftentimes cleansed from the negative commentaries. Releases broken content that causes server crashes for weeks. (Lel that BWL release) Has the biggest playerbase. Like with ED originally, it seems that people are driven by PR rather than rationality. Known also to reboot their server after not hitting population goals (framed later as "beta testings" by PR despite being established French-only realm of the past). If one has to try at least dig something actually positive about Nostralius, they have quite alright movemaps.
Kronos is quite alright. It has sufficient playerbase and some actual dedication put into their scripting, but they have history of re-launching the server two to three times in the past with character wipe after not being considered profitable enough by the main server conglomerate they belong to. It's sort of middle-ground when it comes to quality vs. quantity of people. However their finicky past is questionable.
Rebirth is as is, current uptimes and low latencies have been hitting 13 days straight with reboot and still retains best scripting of the vanilla space, about to start AQ event in near future. Suffers from lack of population due to a couple weeks rollback that happened after previous US manager quit and left rest of the admin team in void without any contacts or information. Didn't help when overhyped Nostralius was released during same time the current team managed to get the server back rolling properly after salvage work on character database. All in all remains the longest surviving vanilla server in the scene and it's developement and quality is based on actual progress over 4.5 years rather than claims of this and that made by PR teams.