Well, I only started converting my vinyl collection to CD once the 1994 remasters came out so I can't comment on the quality of the original CDs. The 1994 remasters were solid and all of them sounded pretty great, capturing the feeling that I remember from listening to those records on vinyl. However, when the 2007 versions came out...wow! The difference really is night and day.
On Duke, for example, you can really hear the congas on Behind The Lines and there's some lovely effects on Evidence Of Autumn, both of which were absent from the original mix. On Wind And Wuthering, Steve's guitar on In That Quiet Earth is something of a revelation and A Trick Of The Tail's Dance On A Volcano has got all sorts of stuff going on during the closing section that was never noticeable before. Even the Hugh Padgham productions, which I thought could never be improved upon, sound better - the laugh on Mama has more echo on it, there's a jangly guitar on It's Gonna Get Better that was never there before.
The records from 1970 - 1974 were always going to sound significantly better, partly because the band's musical vision was hampered by the limitations of vinyl and partly because they never had a decent producer back then. The bum note in Supper's Ready has finally been fixed and Willow Farm sounds much more like The Beatles circa Sergeant Pepper (in a good way!). Phil's backing vocals really shine on The Lamb and there are all sorts of nuances during The Musical Box that have been uncovered.
I would never go back to the 1994 remasters, to be honest. I've copied all of my 2007 mixes to disc - adding the bonus tracks - and that's what I listen to in the car (because the original discs are far too precious for me to risk damaging them while driving on the pot-hole ridden roads of Britain!).