Each antlet will give you a completely self-contained and isolated operating system. That way, an antlet emulates a complete physical server as closely as possible.
The basic choice you will make when creating a new antlet is whether you'll make it an LXC or a KVM antlet.
The general rule is: Make it an LXC antlet whenever possible. If you want to run Linux in your antlet, whatever flavor or distribution, pick LXC. LXC antlets are -- under the hood -- implemented as Linux containers, which are way more efficient than virtual machines using KVM.
An LXC antlet is not to be confused with a docker container. Docker's main aim is packaging applications, whereas antsle's main aim is to provide virtual private servers, each of which look and feel like a dedicated, physical server.
The only situation you need to revert to KVM antlets is when the OS you want to run is not Linux, e.g. Windows or FreeBSD. In those cases, you can create a KVM antlet and run the OS of your choice in it. You can even import VMs from other hypervisors such as VMware or Hyper-V.