I think it depends on if you want to use your computer or not.
Most machines (with or without the computer) will start to add up.
The Sizzix is a bit more time consuming, but you will have to decide how many alphabets you will "need".
I love my Cricut (the small original), but the cartridges are kinda pricey and you can't just have one You can use this one with your computer with a free program (craft room), but many people don't care for it and you have to own the cartridges to use the cuts. but this is mostly a stand alone machine.
Lots of people love the Cameo, but I believe it is only used with a computer and it is a more expensive alternative, but you can use the fonts on the computer.
And there is also the eClips--still pricy--I haven't read much about that one, but I think you can also use the fonts on your computer.