Whether monthly SEO packages or ‘one off’ SEO services are better depends entirely on the site and its particular situation. But, generally speaking, monthly SEO packages are better for most businesses, as this allows them to continuously improve their SEO performance over time. And as you know, SEO (as with any other area of digital marketing) is always growing and changing. To help you keep up with these changes, we would recommend a monthly SEO package over a one-time only service.
On the other hand, one-time SEO services can be great for businesses that already have an in-house SEO department or expert that can help to continuously monitor the site overtime, but need help just to solve one or two issues relating to SEO on your site.