I've never used powder before so can't tell you what's best in that regard,
however in terms of cream, for preventative measures I'd use pawpaw..
If your baby has nappy rash, a zinc based one usually works well, such as sudocrem.
I personally love Amolin.. and it smells great too!
If baby does have a rash and doesn't seem to be clearing up with sudocrem or curash or pawpaw etc, best to start using an anti-fungal coz it might be thrush..
But I usually use Amolin. DS has never had nappy rash but DD used to get it and sudocrem and amolin both worked great..