Replication solutions high volume db

Folks,

I'm thinking of replication tools for high volume site.
Postgres on dual Opteron box. 1/2 GB of data.

Big overnight load of data.
Some inserts during the data but mostly selects.

I think I've narrowed it down to Slony and Mammoth.
Any pro's or con's on one vs the other?

There is the obvious price difference but thats managable if Mammoth
substancially better.

Some area where our environement might stretch a solution.
Some records can be large. Limitied to one table but they can be 40K+
of chraracters in a column.

High volume of inserts coming during nightly load (millions of rows).
These loads are coming in commited blocks of 100.

That cannot slow down the replication.
Our call center agents needs access to them asap.

Any locking issues on the master during the replication process?

Anything else I should be concerned about or things I need to consider?
Personal experiences you have had running either.

tia
David