Easiest Mission is The Party
The Hardest for me were:
1) Loose Ends (where you have to kill all those agents near Ice Cream factory, I hated that mission because they always kept killing me if I didn't see one of them, even with 150% health & armor
)
2) Hit the Courier (I ******* hated those women with heavy guns
)
3) Dildo Dodo (because at beginning I had problems with controlling the airplane, would crash immediately
)
For me the final mission Keep Your Friends Close was much easier than the ones I mentioned in hardest missions, hehe.
But I did pass all these years later and completed game 100%. I think I'm going to replay the game once more.
(haven't played since 3 years)