Buying a machine is complicated. There are unfortunately many factors to consider.
First of all the cricut. Do you like cartridges? Do the cartridges suit your needs? Do you want to be locked into a proprietary cartridge only based system?
The cricut as do the black cat, gazelle, craft robo, eclipse, pazzle and slice all use a mat.
The ecraft does not. However the ecraft does cut better with a stabiliser ( a piece of cardstock under the piece of paper or cardstock you are cutting) but it can be reused infiniately once you know the right pressure settings for the materials you are using.
What type of materials will you be cutting. Each die cutter is different and can cut different things. The most expensive machine, the Black Cat can cut the thicker chipboard as can a couple of others if you purchase extra attachments. The ecraft cannot cut thick chipboard. The thickest it goes seems to be cereal packets.
Do you want to to be able to work with your computer? If so what type of things do you want to do? With all but the cricut you can use programs to use free files found across the internet called svg's (scalable vector graphics). You can also purchase files from different sites where people create and then sell their own designs.
In this way you can use a good mix of free or paid for images ensuring you always have what you need for a project.
Do you want a portable Machine. The larger ones are just not that easy to lug around. The slice, craft robo and silhouette sd are light weight and eaier to carry about.
Some machines have the ability to engrave or emboss objects. Is that important to you?
I chose the ecraft first and foremost because there is no sticky mat to worry about. I have a skin condition (psoriasis) and having a sticky mat really put me off buying one. As between that and a cat who jumps everywhere I figured the mat would not stay sticky long.
The other reason I chose the ecraft was the ability to use any svg file I could find to cut images from. I still plan to buy another image card one day but at the moment most of ecrafts cards don't appeal to me. I have searched out a good few thousand images that I have stored on my computer in categories, ready to cut whenever I need.
So in short personal preferences and what you plan to use it for come into play when looking for a die cutting machine. Mat vs no mat, proprietary vs non proprietary and what types of materials and cost are all important factors.
The point being electronic die cutters are definitely the way forward for crafters. Which machine you choose depends solely on your individual set of requirements. Research well so when you do get your machine there are no hidden surprises in the way of what you will and won't be able to do.
This link is helpful as it explains each machine, lets you know what it can and can't do and gives an estimation of costs
Top ten die cutting machines of 2011 reviews