The technical reasons against systemd are best summarised here. If you are running Debian Wheezy on bare metal or in kvm or as an unprivileged lxc container you can upgrade to Debian Jessie without systemd using the instructions at without-systemd.org

If you have Debian Wheezy in an openvz container (which comes with upstart by default in SolusVM) you can only upgrade to Jessie & use upstart for init. If you try the above instructions you will see the following error :

Bash Code
 
root@vpn:/$ apt-get install sysvinit sysvinit-core sysvinit-utils
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package sysvinit is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  upstart:i386 sysvinit-utils:i386 systemd-sysv:i386 upstart sysvinit-utils systemd-sysv file-rc
 
E: Package 'sysvinit' has no installation candidate
 

If you try to install sysvinit manually & reboot you will have a broken container. Logging in to the serial console will show: Unable to open pty: No such file or directory. Your only option is to use upstart for init:

You can however still have an openvz Debian Jessie container with sysvinit if you begin with a Debian 6 (squeeze) container which comes with sysvinit by default.

• Blacklist upstart in the apt preferences as well assystemd & dist-upgrade Squeeze ---> Wheezy
• dist-upgradeWheezy ---> Jessie

You will still have sysvinit as init & if you install openrc don't forget to backup & / or rm -rf /etc/rc?.d after you have rebooted so openrc begins to manage services.