If I were about to only ride 5 coasters for the rest of my life I would have to factor in how enjoyable they are, how smooth and re-rideable they are and how well the experience compliment each other. After some thought I came up with this list:
Phoenix - The first ride that came to my mind! Immensly fun coaster, super re-rideable, good ol' fun!
Bizzaro (or whatever it's called now) - Tall hyper type of ride, smooth, great airtime and super-lengthy and well mixed up layout.
X2 - Something crazy intense and that differentiates from the rest of the bunch.
Black Mamba - The highest ranked looping coaster in my count. Great layout for an invert and an aboundant of theming makes me never got bored of this ride!
Winjas - Another all out fun coaster and personal favourite :--D