I also prefer a Shimano Rapid Fire shifter to any twist grip shifter. The shifts feel crisp and precise. Rarely overshoot the desired gear. I also prefer the more or less static hand position while riding versus having to rotate my hand/grip to select a gear. It's a personal preference/comfort thing.
My current commuter (MEC Desire) began life with a twist grip (and a Nexus 8 IGH & rim brakes. Currently sporting a Handspun Alfine wheelset & disc brakes). Bought the bike with the intention of replacing the shifter as soon as I got home. Took the beat-up silver Rapid Fire shifter off my shaft drive bike (Dynamic Crossroads 8) and installed it onto the commuter. Vast improvement. I recently replaced that shifter with a nice shiny new black Rapid Fire shifter and restored the original shifter to the shaft drive (cabling on the twist grip wasn't long enough for the shaft bike).