Imo an a14/15 would be easier since they just bolt in and go no need for changing cross members or worrying about clearance or anything silly like that and depending on what sorta power ur chasing they go pretty good. There still a hell of a lot better than a a12. On the other hand a l motor would get some good power but if ur after lots of go why not a sr or ca or even a small v8. It all depends what ur preference. Opinions are like bum holes, everyones got one. In my case i had a a15 it went pretty good but i want more so im going a ca18det. Hope this helps lol