haproxy tends to be lighter weight and higher performance. Also, haproxy gives (as this article mentions) a lot more information regarding status information, which can be used to monitor and manage the applications being load balanced.

Also note that Willy Tarreau has been a Linux kernel guy for eons and does a lot of upstream kernel patches, some of which haproxy benefit from. Most recent example: https://github.com/torvalds/linux/commit/3979ad7e82dfe3fb94a...

Willy also was the long term maintainer of the 2.4 Linux kernel (yes... 2.4), and does a lot of maintenance with the long term 2.6 release. So many embedded companies rely on his trees for their devices it isn't even funny.