Speed,
Since, again, this is not specific, let me address speed in terms of CPU, Disk and Net I/O using Passmark benchmarking. Caveat: benchmarking is not the end-all-be-all, but it is quantitative. The Fusion EULA forbids me to post actual numbers but let me characterize them.
Both products virtualize the underlying processor. Parallels only enables one core. VMware lets you enable two cores. Hmm...
I've benchmarked Fusion's Gigabit Intel e1000 NIC against Parallel's on a wired connection. While I can't give numbers Fusion debug beta is faster than Parallels RC.
Likewise I have benchmarked Fusion's virtual LSILogic SCSI adapter against Parallel's IDE adapter. It's no contest...
You decide.
ease of use,
Pass -- as this is too subjective
device management,
Fusion has a toolbar which shows which devices are present and connected. Many devices are allowed to connected and disconnected live. Last time I checked Parallels (3150) most things are static at runtime...
just all around. Of course, they've been working on the product for a long time, while VMware is just going into beta, so this is understandable.
I'm not trying to argue ad infinitum. If you prefer Parallels, by all means stick with it. I admit I use my production VM in Parallels since my Fusion VM is disposable (well - backed up) during the beta. I've (ab)used my Fusion VM and it keeps on ticking.