Don't have either really.
Disagree on that it's bad to have them both as the same person (and that person also being your only best friend). I'd say it's only bad if you're the sort that really needs a best friend to sort out your problems and feelings.
It really depends on how you react to problems in the relationship. If you're the type to seek a shoulder to cry on or a trusted friend to talk to then it's vital to have a best friend who isn't also your partner. If you're the type to seek some alone-time and just think things over quietly then it doesn't really matter I'd say.
Disagree on that it's bad to have them both as the same person (and that person also being your only best friend). I'd say it's only bad if you're the sort that really needs a best friend to sort out your problems and feelings.
It really depends on how you react to problems in the relationship. If you're the type to seek a shoulder to cry on or a trusted friend to talk to then it's vital to have a best friend who isn't also your partner. If you're the type to seek some alone-time and just think things over quietly then it doesn't really matter I'd say.