Coaster -
Negative intense: Condor at Walibi Holland, I hated every moment of it, it was shaky and uncomfortable and just absolutely terrifying, this was also my first experience with inverted coasters which resulted in me crying like a baby first time I was about to go on Black Mamba at Phantasialand (which - now - just happens to be my 2nd favorite close after Helix). I went with ThomVD who just sat there next to me laughing the whole ride...
Positive intense: Helix at Liseberg and Black Mamba at Phantasialand, just absolutely fantastic rides. Especially Helix in the dark. And Black Mamba with all its foot choppers, both are great rushes for sure.
Flat ride -
Negative intense: Talocan at Phantasialand (or any other topspin) I just don't like the concept of spinning upside down (or any direction really) "uncontrollably", like a few inversions here and there isn't a problem I actually quite enjoy it, but there's a point when it just gets too much for me, and topspins are such points.
Positive intense: It probably seems really lame but I find Jukebox at Liseberg a great intense flat ride, it has some weird G's and spins a fair deal but not too much (see the above comment on Talocan).