My first post!

DiMeo is in effect the boss throughout the entire series as the show never mentioned him dying or abdicating. "Beppy" Sasso was the "aging underboss" in Season 1 until he got busted at the end of the season. At this point it was Junior as acting boss and Beppy as underboss with consigliere unknown and possibly vacant (the upper positions could have been jailed along with DiMeo). Some have suggested that Mikey P acted as consigliere for Junior before his demise. Once Junior and Beppy went to prison, Tony took over as street boss/acting boss and Paulie took his crew over.

Tony was never mentioned as being underboss of the crew but it could be assumed that he is once Junior is out of prison and in house arrest and, more or less, a front boss for Tony. Sil is consigliere at this point. Once Junior starts to go a little nutty, Tony officially takes over as "acting boss" with Sil staying on as consigliere and Bobby being bumped up to underboss.

This is just my interpretation so don't take it as gospel.