Another possible log shipper is nxlog, it compiles to native code and does not have any noticeable impact in terms of CPU or memory usage on my various low-end servers.
I used to use nxlog to collect Windows AD logs to a Linux server. Often, it would end up deadlocking (2-3/week) on the Windows Side and would stop shipping the logs. It was very useful to have the logs but I'm very glad we were able to replace it.
On my servers I use the open source version of nxlog to collect various logs and forward them to a central nxlog server, which in turn feeds logstash. Behind logstash I have configured elasticsearch as storage and I use kibana as a GUI to search and browse.
We've had no issues with rsyslog, which already comes packaged in ubuntu. Runs with no issues on micro instances on the AWS cloud, even at heavy workloads.
http://nxlog-ce.sourceforge.net/