Well, both products have their strengths and problems. As a longterm customer of Parallels Desktop (from the first public beta), I must admit that the quality of Parallels Desktop is poor and the support is nearly non-existant :-(
As many posters here already mentioned, they liked Parallels but have enough with ongoing stability issues and false promises. Personally, I think Parallels is feature driven and don't look for perfect stability as VMware does.
Only take a look at the official blog for the latest Beta : "As we roll through subsequent betas, we’ll be adding some other really cool, never-before-seen-anywhere features, so keep an eye on the blog for updates."
They tell about features, more features, never-seen-before features ..... where is the stability ? Normally, you'll build upon a good foundation, but...
I use VMware products alot in my company (ESX, Workstation on Win and Linux) and I migrated my Parallels VM's over to Fusion while it was in Beta3 ... not a single crash, only one minor problem. I don't need all this stuff like Smartselect, DirectX etc., just a stable platform to run WinXP, Novell Open Enterprise and SLES servers. Please note that these VM's are critical for me and I needed to reboot my Mac at least one time a day with Parallels (lost network connectivity).