The licensing costs between 2012 & 2014 are not severe such as they are between 2012/2014 and all the rest of the older versions of SQL Server. With that in mind, I'd just go for the 2014. It's not going to cost so much more that it hurts, and you'll have access to more and better functionality as well as a fantastic new cardinality estimator (first one since SQL Server 7 back in 1998).
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning