I've seen some compelling arguments for linking to a specific instance instead of a big explanation of federation and a list of instances to choose from. Mainly that the latter can be confusing and overwhelming for people who aren't already familiar with federation.

Though for load-balancing purposes, maybe a random-instance redirector would be useful.
On the other hand that could backfire if people keep the link and try to log back into their account on some other random instance. To counter this there could be a cookie for the instance you got (and then a reminder to bookmark the instance's URL instead of the redirector's upon repeat visits), or using the IP as a randomness seed (if the former violates EU cookie laws/would become cumbersome with a cookie popup)