It looks like ext-rdkafka is going to be the future standard, but is currently in alpha and cannot be used without packaging. Try to find another library that stays close to the librdkafka bindings, to make future migration simpler.
Supports Kafka 0.8 and 0.9, designed as a thin binding layer above librdkafka. This is the only Kafka extension to make it into PECL. However, the extension is lacking glue to compile under HHVM.
nmred/kafka-php -> We've chopped the consumer bits out and made some big changes, so the WMF fork is not suitable for this project. The package itself is PHP-only, but the consumer has a dependency on andreiz-ZooKeeper, which is a binary extension.
Exploratory integration with nmred/kafka-php: https://github.com/adamwight/php-queue/tree/kafka
https://github.com/hauptmedia/php-rdkafka -> Wrapper around ext-rdkafka, which might be nice in the future. Only one contributor so far.