Windows servers have all the downsides of Windows anything, patches, patches, updates, all the time. But your provider should handle that (unless you are reselling on a VPS)
Where Windows has the edge is with large corporate features like Exchange (and as mentioned if your site builders use asp) The thing there is if you are a big enough company to need Exchange and those type expensive features they probably have their own servers and IT department.. not a market for resellers. :disagree:
To me it would seem the biggest benefit is to get customers who use the Expressions packages to build sites and must have Windows to get the benefits of all their "goodies". However Expression hasn't taken off like Microsoft hoped that I have seen (haven't seen a lot of sites with it). It mat catch on but I think Microsoft waited too long with FrontPage before introducing Expressions and while it has some cool features that will work on Microsoft servers to build the high-end web sites like the corporate stuff as far as basic customers like a reseller would have Deamweaver and other platform independent programs grabbed the lion's share while Microsoft went years between FrontPage and introducing Expressions.
I tried the free 30 day trial of Expressions and for the "average" web site it sure looks a lot like Dreamweaver to me.
So as a reseller I don;t think it makes a difference if you want Windows you will pay more generally and most people who would buy from a reseller would tend to be the people who use the highly popular open source stuff out there these days like WordPress and Joomla etc. Usually all those come bundled with the auto-installer Fantastico on a Linux machine although they are often a version behind, so sometimes a client may get a site and immediately have to upgrade.
It's whatever you feel comfortable with :shaky:, there are also the differences in control panels & other software for the two. So find some places you can test drive a demo of whatever control panel your prospective hosts are offering.