If you're a MSP, Intronis is a no-brainer. We've been a partner for over two years - their support is great, pricing is fair and they have a full white label for your software. The software is a little slow (gets unresponsive when it's working in the background at times), but seems to be improving with each release.

Don't look other places - if you're serious about providing a good backup experience for your clients, take a look at Intronis.