I've run both, mainly because even the Fusion beta wasn't available when I needed VMs for work under OSX, so I bought and ran Parallels for a year or two. My initial impressions of Parallels was pretty good, actually, and when I later moved to Fusion beta then 1.x, 2.x, there were some occasions that it seemed that Parallels had slightly better performance, but I never did benchmark both of them on the same machine, so was 'by feel' only. I think this was Parallels v1 through v3, now they're at 5.x or something, and went through Fusion 1.0 beta through today, 3.x.
The big benefit of Fusion is building VMs locally that I can share among Windows and Linux VMWare users, as well as VMs that can be deployed to ESX servers if needed. VMWare has various line tools/utilities available, like vdiskmanager to grow your virtual drive, which is occasionally useful - not positive if Parallels has the equivalent, but wouldn't be surprised if they did. Parallels had hardware/GPU based graphics acceleration first, then Fusion added that. full-screen 'unity' mode isn't too appealing to me personally, not sure if parallels has that today or not. If it weren't in my interest to retain VM compatibility, and didn't have a history around 10 years with VMWare, I'd take a look for some recent benchmarks from a reliable source, check the recent features for anything you may think is important, and see who's running a better sale at the time.

I'd be surprised if they're not fairly close to party with each other feature-wise, and likely within 10% or so on performance. I can't speak for consumer level customer service, although to run a single VM, I also wouldn't expect much is really needed, although vmware does have a large set of online communities backing up any 'official support' if needed.
Try virtualbox if you just want to see how many resources it will take and in general, how well a Windows VM may run on your system/specs. I haven't run virtualbox in at least a year or more now, was OK, not quite as 'works out of the box' as either commercial offering, but it is free and worked reasonably well.
Sorry, probably not much help..I don't think you'd have real issues with either.