Curious: if you were going to switch, how would you want to run this? Would you want to deploy it to your own EC2 instances, or would you want a hosted solution (just as SQS itself is?)
Unless you need the features, I would steer away from the "real message queues". Running these adds complexity, especially if you want higher availability and they are not always cheap.
HTTP based solution is easy to understand and implemented (if basic functionality is enough for your use case). Real MQs obviously have more complex protocols and not all client libraries are perfect.
I find basics of most AMQP systems to be extremely reliable. Message on, one time delivery with message hiding until expiration of TTL. Sure, you can get into some insane setups with RabbitMQ/Kafka and that's where libraries features don't always match up. But SQS probably wouldn't work for you either in those cases.
