The best replacement for logstash is splunk.

The best alternatives to logstash are rated as following:
★★★★★  splunk
★★★★★  fluentd
★★★★  graylog2
★★★★  flume
★★★★  kibana
★★★  loggly
★★★  syslog-ng
★★★  rsyslog
★★★  syslog
★★  kafka
★  lumberjack
★  scribe
  riemann

Your alternative for logstash is not listed? Suggest!
Speaking about logstash, one probably shouldn't forget about elasticsearch.

Other search terms related to logstash and their ratings are:
★★★★★ elasticsearch
★★★★★ redis
★★★ rsyslog
★ graphite
★ kibana
graylog2
You have in mind a companion for logstash and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of logstash in all years. Click on graph for more.
logstash
splunk
fluentd