It depends what you are expecting out of the machine. The Imagine is the newest cutting system offered by Provocraft. I do not have it but I have read about it in the forum on cricut.com. It has had a lot of negative talk about it not doing all the things it is advertised to do and is limited in it's ability to do certain task such as moving around on the mat, working with the gypsy, etc. This machine has additonal cost of replacing ink cartridges. The cost of the machine is quite high as well, but I have seen it as low as 299 on the cricut site. It can't be moved around without having to recalibrate it and as of now only cuts up to 12x12. So for me the cons out weigh the pros which are that it prints and cuts and has carts that contain patterened paper images and you can get the exact color you need with RGB codes.Someone who has an imagine may give you more info on this machine. It just is not for me.
I have the expression and a baby bug (my kids). The expression is not as expensive as the Imagine they are 175 on the Walmart site (alot less then I paid for it) and can be purchased cheaper on EBAY and when the E2 launches I expect the price to drop more. I love this machine because I am a paper addict. I like having a huge stash of paper to choose from when cutting images. The expression is a cartridge based cutting system that allows you to pick the size and colors of any image on a cartridge. For cardmaking it has a lot of great features like auto fill which allows you to cut multiple images on a mat. You can cut up to 23 1/2 inches. Materials that need replacing are mats but you can restick them, blades, and you can get caught up in collecting cartridges. I have 60+. I also use a third party software with my expression (scal2 it increases the cricut's creative ability tenfold) which is not allowed by provocraft and currently there is a lawsuit to try and stop the ability of use with the cricut. I hope you understant the rambling I have offered you on my opinion of the 2 machines.