What is the recommended Mac desktop VM software for Linux guests?

I use a MacBook Pro as my primary machine, but my work targets Linux servers. I'm currently on a project with multiple dependencies, and which is configured for Ubuntu.

1. Configuring all these dependencies on OSX is a pain. I've been through Macports, Fink and Homebrew. They are all nice, but they don't provide a 100% drop-in replacement for Ubuntu packaging. Rewriting all the deployment scripts just to accommodate one Mac developer seems like a waste of time.

2. Dual-booting Ubuntu on this Mac doesn't seem like an option yet. The current hardware generation (7,1) is not fully supported.

3. Using an Ubuntu VM for all my development work seems to be the way to go. I'm using VirtualBox at the moment. Seamless mode is nice, but I wonder if VMware Fusion or Parallels will be nicer.

So here is the question: what's the best VM app for Linux desktop guests on a Mac OS X host? VirtualBox, VMware Fusion, Parallels, or any other? What do you like about it?

Update: Learning some hard lessons:

1. VirtualBox disk images are not resizable. VMware Fusion disk images are.

From serverfault Jace

• I use VirtualBox only for running virtual MacOS instances and VMWare for the rest, but in general I consider at least VMWware and Parallels equally good for my use. I can't say this about Virtualbox mainly because I don't use it much (except, as said, for MacOS virtualization), but it at least has the advantage of being free.

  For Linux, both VMWare and Parallels work nice, so pick whatever you want. VMware has the advantage that you will get much more ready made virtual appliances for it than for Parallels, but that might not be important for you.

  : I switched from VMWare to VirtualBox some two years ago. The problem with virtual box is that they want you to buy the full (closed source) edition and therefore important features (like USB support) is missing. Another thing is that after Oracle bought Sun the future of VirtualBox is unclear. I consider switching back to VMWare.
  From SvenW

• I daily use VMware for virtualization both for testing purposes and production.

  I have chosen it among the others mainly for its stability and the fact I can use the same VMware VM as is in a cross platform environment. I.e. I have some XP VM being used for customer assistance, Debian machines to have a portable cobbler server being able to install other machines (bare metal or virtual is not a matter).

  On Mac OSX then, the "Unity" feature of Fusion is very very amazing and help in integrate virtualized applications into the native OS.

  SO, my suggestion is VMware Fusion.

  Jace : Does Unity work for Linux guests? What version of VMware Fusion is this? I have a license for 2.0, but will need a compelling reason to upgrade to 3.0.

  AlberT : No unity is for Win guests, sorry I was enumerating different features I found good, not only those being useful in the question scenario.
  From AlberT

• Perhaps this question is more appropriate for Super User. Asking again there.

  From Jace