entirly depends how you define your meaning of better !
if you stay in the vag box you can have 20vt, TFSI, v5 or vr6 and it's relations. depending what you want from it any one of said engines chould be the best conversion. the magor advantages for the ABF is it's bolts up an works without much bother, it's proably the best bang for buck conversion into a golf 2. the enigne is tough and there isn't really much to go wrong with them. seem more popular with the trackday crowd than 20vt's probly for those reasons