Evaluated both VictorOps and Opsgenie. Both of them were so-so.
Like u/michaeld0 mentioned, the on-call options were not as flexible as I would have liked it.
We're currently evaluating Squadcast and it looks quite promising. Found their on-call rotations to be very flexible and they also seem to have few readily available incident postmortem templates which we found useful
You should definitely check out Squadcast - https://www.squadcast.com/
Its way better than PD or OpsGenie for a bunch of reasons.
i) Completely free to use for up to 10 users - Their platform is the easiest to work with, and their team truly empathises with the pains of being on-call.
ii) They've got great push notifications and native apps on both Android and iOS that alert you on the go, so we chose to turn off all email, phone and text alerting. Gotta love this. Slack is still on though.
iii) Very simple scheduling and rotation management that your grandmother could use.
iv) Reducing noisy alerts is straightforward with deduplication rules to suppress repeated alerts, and automated tagging of events.
v) Very cool things you can try like automated post-mortems and public service status pages. Although this is not super mature, yet.
vi) Scheduled maintenance that can be repeated weekly or monthly, which records all events but turns off the pesky alerting.
I think Squadcast is one of the top PagerDuty alternatives. Though some features from PD are missing, you'll find that its cleaner and simpler to use. Moreover, if you're into Site Reliability Engineering (SRE) it is one of the best SRE tools out there.
Other more popular alternatives like Opsgenie and VictorOps are also quite advanced.