If it is sending some emails and not others, the issue is on the SMTP Server, not with Universal Email.
You should contact the host to have them look into the SMTP server error logs to see why the email is not being sent.
As far as which email object is better, that depends on what email objects your host supports.
The Pear Mail for SMTP object in some cases is better, but it depends on whether your host supports it or not.
Organization and x-mailer are optional headers.
You can set orginization to the name of your company. if set, xmailer should be set to 'PHP Script"