Between H-Sphere and Plesk - wow - this is a tough decision. Plesk is an outstanding control panel - however, it is still a little immature WRT clustering and dual platform.
H-SPhere is a little more established and proven with dual platform hosting (linux and windows) as well as their clustering ability and history.
Having said this, I really do not think you could go wrong with either. Also, I think you are on the right path with Plesk/H-Sphere, as you really want the flexibility of Dual Platform (even if your primary platform is Windows) - I do not believe other Windows Hosting Control Panels, including Helm, offer this capability.
I'm doing Linux hosting (or will be soon), and am new to this whole thing. I won't even have installed H-Sphere until the next server arrives tomorrow.
Having said that, in my opinion one of the strengths of H-Sphere is that it can manage your accounts on multiple servers, so if a server gets overloaded you just have H-Sphere rsync to a new server, update the nameservers, and delete the old files -- all without any hassles from the client's perspective.
Expand this a bit if you run into trouble with one provider, buy new boxes on a second provider, and migrate ASAP and you seem to have a good "out" in case something unannounced and unexpected happens.
Add in the billing and management features, and it seems like a no-brainer. I just wish it'd do clustering for redundancy reasons as well (as in keep multiple servers in sync in case one fails), or maybe loadbalancing...
I just wish it'd do clustering for redundancy reasons as well (as in keep multiple servers in sync in case one fails), or maybe loadbalancing...
It can most certainly handle this... The most obvious is with DNS - as any responsible cluster admin has NS1 and NS2 separated on different servers for redundancy - additionally, it is not overly difficult to cluster and load balance resources like mail servers to achieve an even higher degree of redundancy amongst your clustered services...
I have only used HELM and Plesk, and personally I like Plesk more. I read someone calling it immature - and I can see where they are comming from, but from a client point of view, I think that they will feel more comfortable in Plesk.
I haven't used H-Sphere, so I cant speak for that, but I have heard good things.