Regular SAM. mobile SAM's can be degregated and you need more to have the effectiveness of a SAM. Better is both SAM and 4 jets on AS. Best is SAM, 4 mobile SAMS, and 4 jets on AS. But who wants to wait for that? With enough SAM's and Jets, AI rarely can keep more than 10..20 bombers. With that few, just mass you troops and keep pressing forward. You may lose a few, but a fast advance is hard for bombers to adjust to. Don't forget you can weaken bombers with counter stealth bomber attacks.
PF