A14 is a better option due to the increase in size. It not only has more horsepower but also alot more torque which is essential especially in the sunny as its a heavier car. Dont spend $600 on a stocka. A fella on here a few months ago advertised a complete A14 including gearbox(and it already had some work) for $200. i know you may not get a deal like this again but just wait around and see. Dont work the a12 either without a rebuild otherwise you will run into troubles when you start to rev the hell out of it as its already worn.

Advise is to go A14/15 if you want it to go decent for less $$$. Put it this way a stock a14/15 will beat a mild a12 and still be easier to drive.

PS. I have an a14 short motor but would require new rings and possibly pistons. Its apart so you could check it out if you want.