He was a smart guy. Also his focus on white collar crimes was more lucrative and less risky than the usual blue collar crimes. I can understand why Carlo chose Paul. Neil was very respected but he was constantly under investigation/indictment and wasnt the smartest guy lets be honest. Also Paul staying away from social clubs was probably the smartest thing despite being hated by those guys. Pauls biggest mistake was probably greed and that he didnt resolve the bergin crew issue sooner.