Here’s an unbiased opinion predicated on experience of testing both, in the event you are seeking to decide between routine Bukkit or Spigot for your server. From a player perspective there’s almost no difference until RAM/CPU comes into play, and that is just going to be an issue if you’re seriously interested in truly being a server admin.
Bukkit is great if you “only require it to function.” So it’s more friendly towards the new server admin, there’s not as many configuration alternatives in Bukkit, it is also not as inclined to go wrong in the hands of someone who probably should not be a server admin.
Bukkit is what Spigot is based on, and the primary direction that Spigot heads is consequently dictated by Bukkit in. That’s not a bad thing, because every boat needs a direction.
If you’re seeking to establish a server at home, or you are new to truly being a server admin, stick with Bukkit until you’re comfortable with every setting in bukkit.yml and server.properties including the ones not establish by default!
Spigot is great in the event you have to tweak things for gameplay or performance. Spigot really excels at enhancing CPU and RAM usage in comparison to common Bukkit, and I have found RAM savings of 100%, where machines have gone from using 650MB to 325MB. CPU isn’t too different and on some systems I’ve found spikes that caused 60% use fall to 20%.
Spigot adds a variety of choices to server.properties, including built-in, configurable, per-world Orebfusticator for Anti X-Ray as well as the ability to control growth rates of harvests, as well as rainstorms frequencies and strengths. All of these things (and more) matter to a dedicated server, particularly with multiple worlds.
Spigot is not for someone new to being a server admin, and there’s probably no point in using it for a home server. Spigot is finely tuned for dedicated servers and it does that job very well.
Why does it matter?
RAM! RAM! RAM! On average, every player on a system uses between 50-100 MB of RAM (based on the server’s view space settings together with other factors).
In the event you’re seeking to run a dedicated (i.e. permanent, not weekend or “until I get bored”) server, RAM is important. It costs money. Without enough, your players endure; too much, your money is wasted.