For running the latest Android 5.0.2 Lollipo ROM, I do recommend CM12 ROM for all Galaxy S3 models for now as you will get the latest updates/fixes as other AOSP ROMs are built on top of CM12’s source code.
Again, for GT-i9300, CM12 is near flawless and I highly recommend the Temasek builds. As for other S3 models, you will have to try the beta CM12 ROMs, which are pretty solid except the camera.
Overall, it’s been a very slow progress for the Galaxy S3 but we should have fully-working Lollipop ROMs soon for all of you without GT-i9300. In the meanwhile, go knock yourself out with these CM12 ROMs. At the worst, you can go ahead and make a backup ROM, try the Lollipop ROM, then revert back to your old ROM.