I have used wu-ftpd for a long time,
despite frequent security issues,
only one of the sites i have seen where compromised.
And that had a 3 year old version installed.
I have seen a good number of sites compromised by proftpd.
At one of such incidents, the problem was discussed on the
proftp mailinglist for 3 weeks, without any anouncment on the webseite.
After 4 weeks tehre was sill no security anouncment for this root-exploit.
Therefore I migrated all sites in reach to vsftp.
Today proftpd has more vulerabilities that wu-ftpd.
I prefer vsftpd now,
very stable and good throughput!
In doubt look at the code inside.