> Is there a more detailed comparison?
There's nothing more detailed that I know of. Is there a particular feature area/comparison you're curious about? I can add a bit more detail.
> It's not apparent to me what the advantage of either interface is. In both situations I have to define a "lambda"
What I meant by this bit is that the user experience is different. Failsafe can be used with method references or lambda expressions [1], which are a nice, concise way of wrapping executable logic with some failure handling strategy. You cannot do this with Hystrix since all logic must be wrapped in a HystrixCommand impl, which cannot be implemented as a lambda.
> either seems acceptable.
Like anything, it just depends on what you want. If retries and general purpose failure handling, consider Failsafe. If request collapsing, thread pool management and monitoring, consider Hystrix.
[1]: https://github.com/jhalterman/failsafe#synchronous-retries
