My favourite is Fahrenheit's Norwegian Loop, purely because no other inversion feels like it. The little pop of airtime before it twists underneath itself is fab.
Controversially, I'm also a big fan of the newer style of B+M Zero-G, as found on the likes of Swarm and Oz'Iris. I love how slow and drawn out the floaty bit is, they're like a tantric inversion <3
Air's Fly To Lie is always an 'oooh' moment for me. I find it weird that B+M never re-used this element in their other Flying coasters, it's such a great sensation.
Speaking of B+M Flyers, their Pretzel Loops are my least favourite inversion. They give me a blinding headache. I don't mind Pretzel Loops on sitting coasters like Helix though.