If you have all your applications 'on prem', you introduce an extra risk by moving your integration layer to the cloud (suddenly your internet connection could bring down your integration layer) but the good news is that you can use Service Bus for Windows Server, that you run locally (even with Windows Azure pack!) The same programming model, similar messaging features, so that might be a good option.
Comparing with BizTalk... Service Bus is light weight, messaging only. BizTalk provides much more rich features (transformations, pipelines, BAM, Business Rules, adapters).
Good luck