I have a Cricut Expression. I love it because it is very versatile and you can cut exactly the size you want. I don't know much about the Slice, but I've read good reviews. It doesn't appeal to me because even though it looks like it has some cool cuts, it is very limited in the size you can cut. Manual machines also do not appeal to me because of the limitations on size.
I did a LOT of research before I settled on the Expression. It just fit me better. I love being able to cut titles or letters at any size that I need for a particular project. I also like that while it is independent of a computer, you can use it with a computer for even more variety.
Good luck on your venture!