Which AWS Direct Connect region should I choose for a connection in Slough?

For a UK-based workload, eu-west-2 will usually be the natural choice because it is the London Region. eu-west-1 is in Ireland and may still be appropriate if your applications run there. Check the Direct Connect and data-transfer pricing separately rather than assuming the region option alone determines the total cost.

The main factor is where the workloads and VPCs are located. eu-west-2 is the London Region, while eu-west-1 is the Ireland Region, so choose the one that matches the resources you need to reach. The physical connection being in Slough doesn’t make the two options Availability Zones.

Those labels are AWS Regions, not Availability Zones. Availability Zones would look like eu-west-1a or eu-west-2b. For Direct Connect, the selected region is associated with the AWS routers and the control plane, and some colocation facilities can offer access to more than one region. If you’re using a Direct Connect Gateway, the choice generally matters less, although choosing the region closest to your workloads is sensible. If you’re associating a virtual interface directly with a VPC through a virtual private gateway, the region needs to match the VPC’s region.