2014 BRZ Turbo if you can wait and see if it really does happen. If not BRZ now.
In order of most speed/power in a straight line stock vs stock
1. MS3
2. Gen coupe V6
3. Gen coupe 2.0T
4. BRZ
As far as handling in order of which is the best
1. BRZ
2. MS3
3. Gen Coupe V6, Gen coupe 2.0T
If you plan to mod, in order of most aftermarket support
1. BRZ
2. MS3
3. Gen coupe 2.0T
4. Gen coupe V6
If you want to stay relatively stock and care more about power and utility, get a Mazdaspeed3.
If you want the absolute best handling car in stock form and want a real sports coupe, BRZ.
I've got experience with the Mazdaspeed3 as well. Go to my site
www.crossoverauto.com to see the parts available for the MS3 and BRZ. Either way you go, let me know if I can help.