Newer Version of SQL Server Less Stable?
You obviously don't need my confirmation but I can't think of a single possible reason why I would suggest to a client they go with 2012 over 2014. Particularly for support / end of life reasons, but also because of additional features and enhancements to existing capabilities.

Some reasons you might hear:


Performance degradation. Sure, this can happen, but it can also happen when going to 2012 or making any other major change (some of the reasons can also be attributed to migration without upgrade, failover, etc). Regressions are an expected part of change, and it's easy to blame an upgrade (just ask the VSTS team).
Higher cost. I've seen a few claims that 2014 costs more than 2012 for the same configuration, but haven't observed any licensing changes that would cause that to happen except that standby secondaries now require software assurance to be licensed. The other aspect is if someone without SA planned poorly and bought 2012 and now wants 2014 - yeah, that's going to cost them.


Generally worse performance? Less stability? No, both seem laughable to me. Ask your drunk friend for some real evidence, and maybe keep him distanced from clients, too. :-)