Pussy, barring him being an informant, would've made a capable Boss. Paulie of course not.

Richie wouldn't have lasted five minutes as a Boss; he was barely respected even as a Capo after he got out of the can, because of his temper and lack of respect for the current status quo. He was also too old fashioned, too stuck in the old ways, to last long. He wouldn't have the intelliigence to think up complex schemes like the HMO scheme Tony thinks up, or to turn the Esplanade into a gold mine. He'd have stuck to the old things--Sanitation, drugs, extortion, trucking, etc. In the 70s, 80s, he probably made a great Capo; prison probably messed with his head, along with the fact that due to being in jail he was in essence "passed over" for Boss first by his kid brother and then by Tony. Richie'd either have been killed or would've been picked up by the Feds quickly.

Guys on the show I can see being a good Boss are:
Patsy Parisi (low key, cold, calculating, smart, got balls)
Larry Boy (If not under house arrest, seems pretty smart)
Feech (hot tempered but also very traditional, greatly feared and respected, smart)
Vito (if it never came out that he was gay; he was a very decisive, calculating, highly intelligent guy, savvy, cold blooded when need be, and an amazing earner, who also had a close tie by marriage to New York. Phil seemed to have regard for him before he was outed.)
Albert Barese (Yes he repeats himself but he also showed himself to be smart at times. He was the only one who figured out that Tony killed Ralphie over the horse)
Ralphie (If he wasn't coked up and psychotic. The guy had brains, balls, savvy, the best earner the family ever had, he just needed more self control)
Gigi (Level headed sort of guy)
Tony B. (If the hijack had gone the other way, he probably would've been Boss. He was smarter than Tony S., less of a boorish asshole but also still very street smart and respected before the Leotardo incident, he was considered a "rising star" before he went away)