Single long-ester testosterone for the win. Sustanon was intended to provide for more stable serum testosterone levels, but what was intended doesn't pan out as true.
Once of the test esters in sustanon is testosterone decanoate, which is a long ester than cyp or enan. test deca by itself would therefore provide more stable levels, but it just isn't popular ... one reason for this is that people would confuse test deca with what 'deca' usually is used to describe: nandrolone decanoate.