BBMs in various forms, depending on your goals and budget. I also use the ED Pro Ports, again in various forms depending on goals and budget. The OE 427 blocks hold up surprisingly well if prepared correctly. I have several customers right around 800 hp with non-filled OEM 427 blocks.....some have run for years with no block issues.
The 428 blocks start to get cost-prohibitive when crossbolts become a requirement, and won't live as good as a 427 block even if cross-bolted.
There are smart guys around here with Bbbbbrains who do not begin with B......like JC.....