Short answer
If you mainly need written ownership and title information, order the Title Register. If you want both the written register and the plan showing the general registered extent, order Title Deeds on this site.
Official source: https://www.gov.uk/search-property-information-land-registry
When the Title Register is enough
The Title Register is usually the starting point for owner details, tenure, title number, charges, rights, restrictions and other written title entries.
Official source: https://www.gov.uk/get-information-about-property-and-land/search-the-register
When Title Deeds may be better
Title Deeds is a customer-friendly combined order for the Title Register and Title Plan where available. It can be useful if you want ownership information and the plan showing the general extent of the registered title.
When you may need something else
If you need a historic conveyance, lease, transfer, deed referred to in the register or formal official copy for a legal process, extra checks may be needed.
Official source: https://www.gov.uk/guidance/land-registry-portal-how-to-request-official-copies
Independent service note
LandRegistries.com is an independent document-ordering service. It is not HM Land Registry, GOV.UK or any government department.