If you're buying (not leasing) and plan to keep the car for a while, the last model of a generation is generally better than the first model of the next generation since the majority of the "kinks" have been worked out. Take, for example, the first model of the third generation WRX (2008) - the TD04 turbo was scrapped for the more powerful VF52, or the first model of the second geneation STi (2004) - the 5x100 lug nut pattern was scrapped for the larger 5x114.3. Toward the end of the second generation, the WRX began receiving the larger 2.5 L engine from the factory instead of the 2.0 L prior to 2006. There are a number of other examples...
If 2014 is going to be the first model year of the fourth generation line of WRXs and STis, then you might want to wait until 2015 or 2016 just in case there are any significant changes in the following year or two. If you can't hold out that long, I'd recommend going with the 2013.