It appears that both provide latest Word/Excel/Outlook/Publisher/Powerpoint with 1 year subscription.
But there is a bit of difference between them. MS Office 365 Pro Plus is about $150 a year per user whereas with Small Business Premium (<$90 on amazon.com), you can install it up to 5 PCs or devices. It is the same software, if I am reading it right.
What would be advantage of going with Pro Plus over Small Business Premium?