I have used both and for my requirements Londiste is a good option.
We have a simple set up where a subset of tables is replicated from a staging server to live by large batch updates and insert and also intraday smaller updates running on postgres 8.4 and Centos 5.5 and skytools 2 and we also use it as the queue component for event based actions. Previously I have used Slony from the 1.* series so I can't comment on more recent versions.
Some Pros for Londiste
- Simple to set up
- Generally simple to administer
- Haven't had any issues with robustness of replication in 8 months of production use
- Also can be used as a generic queing system outside of replication and it is quite simple to write your own consumer
Some Cons
- Documentation is pretty scant
- You need to be careful when implementing ddl changes
- It won't stop you from making changes in the slave
- Can't be used for cascading replication or failover/switchover use case
I will limit my comment on Slony to my experience that it was complex to set up and administer and the version I used did not compare favourably on tolerance to network issues with Londiste but could have been used for cascading replication and switchover use cases.