Hmmm.... I think it's going to be hard to compare and electronic die cut machine (Cricut) and a manually operated one (Cuttlebug, Sizzix, etc). I have the small Cricut and the Big Shot and I love them both to death.
What I love about Cricut is that the variety of sizes and combinations you can cut with one cartridge. It is also great for "mass production" of projects. For example, you need to make 50 invitations (all the same design). All the pieces you need can be cut in just a touch of the button, and while it's cutting, you can do other things.
As for the manually operated die cut machines, you can do other things with them aside from cutting, such as dry embossing. And most of them can accept dies from other companies. However, you are limited to the size of what the die offers, especially when it comes to the alphabets. If I am to choose between the Cuttlebug and the Original Sizzix machine, I'd prefer the Cuttlebug.
Those are my few cents... I hope that it helps
Good luck!