We currently use Helm. I have used PLesk on both Windows and Linux and I've found it to be very clunky.
Helm has improved tremendously over the last 18 months and has benefitted greatly from a fatstic community on their forums and interaction with the owners and developers.
Helm 4 is due out in the last quarter of 2005 and is set to be a lot more condusive to add-ons.
The main advantage Plesk has over Helm at the moment is that it is dual platform. Once Helm 4 is released it will be easy for developers to build new service providers and there has already been talk of Linux connectors for running Mail, DNS services etc. Hopefully we'll get a Web connector too.
The major difference with helm over other CP's is that it is a true multi-server Control System. You have one point of control and can add servers and distribute Mail, DNS, Statistics, Web, Database services etc across multiple servers to expand very easily from a single to multi server setup. There is no need for every server to be standalone. New servers become part of the Helm controlled network.
Mick Beeby www.reyaltec.com - Quality Helm Dedicated, Reseller & Shared Windows 2003 Hosting. UK & US based servers. www.aspbite.com - Modular ASP Content Management System
We also use Helm and have been very pleased with all the support. I will say the billing portion is a bit lacking (but that is because of WorldPay) - we lease per month and have had a horrific time lately.
HELM is the standard in windows. We use it and from all I've tested it seems to be the best. I've tested plesk a year ago and it was a very bad experience even if my hosting servers for unix are all with plesk but I can't recomend it for windows, there is also h-sphere but I never used it althought the reputation is good. There is also Ensim for windows Hosting Controller and Hosting Accelarator but there are more so the list is good.
I don't think Helm is a standard for Windows. Not saying Helm is no good, but at current, I don't really think there is a dominant player in Windows Controlpanel industry yet. Been using HC for years found it easy to use just that its interface is far less attractive than Helm but its features are much more. I would say look out for Plesk Windows, they have very very strong backing from sw-soft. Maybe in the times ahead we will see a much better Plesk CP for Windows.
im currently trying out helm on our development network, and there are a few things im not 100% sure about... there doesnt seem to be any control for the end users. There is for admins and resellers, but not the user accounts.
I went from setting things up manually to Plesk then to Helm. I found that the windows management of Plesk was too linuxy. They are just a company with marketting rather than a company with a good product. My Linux friends say their linux one is ok. I wouldn't recommend it for serious windows hosting, not after my experience of it.
Helm has been a completely different level. Absolutely love it and more so, love the direction it is taking. I can see myself growing very well with that company.
I find Helm and Plesk to be the best amongst all the available control panels for windows servers.
If I had to choose any one from the above two, I would choose Plesk.
Although you wont get billing manager with Plesk as you get one with Helm.