I've used: XenServer (from Citrix), straight XEN, VMware, Microsoft's Virtual Server (and their new version based off Xen), and VirtualBox. My current favorite right now is VirtualBox.

The current version of VMware opened more ports than I was comfortable with on my box, and had a web based interface. The older version of VMWare gave me problems installing some linux distros.

Xen is great, but doesn't pass USB to the guest very well. It also doesn't have a standardized gui. Which not a show stopper, is nice to quickly with some things. XenServer had the gui, and made doing the things easier, but the underling CLI has been changed by Citrix, so the straight Xen CLI commands don't work.

VirtualBox has done everything I needed it to so far. The hardest part was setting up the "Internal Network". Which is a network that allows the guests to talk to each other without going through the host.

As was said higher up:
If you have the time to, try them all out and see what fits your needs the best.

DANG, i cant get info to paste from my virtual guest to my main host. I was going to use word but thats why i went with google docs cuz at least in the machine i can access it. I do not have BT2 installed,its just running from the ISO in VB. maybe thats why i cant paste to and fro.

I have been working with VB forums, cuz i cant install the additions or guest tools. They are assuming its because my VB's are using ISO files rather than an install. An i have no idea how to install the ISO of BT to my drive.. haha

thanx

I didn't have a problem installing BT 4 on VB (I have it installed at work and at home).
in the gui:
 create new, set it up with linux, linux 2.6 (or ubuntu for BT4), create new hard drive (make sure boot hard disk is checked), select your size, I usually use fixed.

Make sure you have the iso under file>virtual media manager CD/DVD tab.

Click the guest, go to settings, make sure the iso mounted to the drive under storage.

Boot, (drops you to a root prompt) startx, double click the install shell script icon. Guided - use entire disk, IDE1 blah blah blah VBOX HARDDISK

For the guest additions afterward, you have to change the cd (can be done by clicking the cd icon on the bottom of the guest screen), mount the disk usually mount /dev/cdrom /mnt will work. cd /mnt  to get to the directory then ./"filename for your version of linux here"

installed and done. total time roughly less than 30 minutes (depends on the memory of the virtual machine). (doing it on my fedora box at work while typing the post).

Hmm, cant get the guest additions to install at all. It says that i have to force mount them and then when i do, it kills my x session and server. Once it kills it, startx command outputs a bunch of fatal errors. I have BT4 installed to the drive so it is not reading the BT4final.iso file anymore. Which is good.

i made sure it was pointed to bt4drive.vdi and not ISO. i removed that from virtual media manager. So i know it booted form the drive. The cd icon in the bottom right shows guestadditions.iso but still asks to force mount..

its very strange.

thanx