Hi there,
I do agree with Florry, but if you absolutely haven't any spare days to go I would base my decision on who you are going with and what they like to do.
If you have animal lovers the AK is not to be missed. As florry says, it's a lot more than a zoo but if I had to miss one park out it would be this one (I'm not a huge animal lover!)
There are some really cool thrill rides at MGM. Also some fantastic not-to-be-missed shows - if any of your party like going to musicals / the theatre I would not miss MGM.
Epcot (my favourite park

) - can sound quite cheesey when described, but it is a fantastic place with some great thrill rides, lots to see and do and anyone with even a vaguely passing interest in seeing different places / cultures will get a kick out of World Showcase. Oh, and Illuminations is simply not be to missed!! This is a nighttime fireworks / laser / musical show and once seen will never be forgotten!
MK - well this is a must do if you have any children in your party and actually probably still a must do even if you haven't! There is something quite magical about the MK - the atmosphere is something else! There are still a couple of good thrill rides here - Splash Mountain, Space Mountain & Big Thunder Mountian are really good fun.
Not sure if that helps or not, but may help you decide which (if any!) you can bear to miss. If you haven't already got a copy, I recommend Simon Veness' Brit's Guide to Orlando which will give you more information about the above and help you decide.
Cheers
Karen