For those in London wondering where is best for UK based customers, here's an EC2 ping [1] comparison of Frankfurt and Ireland AWS:
Europe (Ireland: 25 ms 27 ms 24 ms
Europe (Frankfurt): 39 ms 39 ms 42 ms
Suggests Ireland is slightly faster. Obviously just a sample of 1 (more data required), but given Dublin is roughly 300 miles away, and Frankfurt is roughly 400 miles away, it makes sense.
[1] Hitting ec2.eu-west-1.amazonaws.com vs. ec2.eu-central-1.amazonaws.com.
The channel is a good rule of thumb. For consumer isps eu-west should be faster in the uk. On continental europe, africa, and the mideast eu-central will probably be better. The notable exception is france, there it depends on the network as to whether eu-west or eu-central is less latent. Either way its normally +/- 20% or 5ms.
Or just ignore all that and use route 53 latency based routing for your dns records. It will return the record for the least latent endpoint, per client.
[1] Hitting ec2.eu-west-1.amazonaws.com vs. ec2.eu-central-1.amazonaws.com.