Back in '95 when I bought my first mountain bike, I compared bikes with Grip Shift shifters and Shimano shifters. The bike that felt better to me ridewise was equipped with Shimano shifters but I preferred the Grip Shifts that were on the other bike. I bought the bike I liked better and the shop swapped out the Shimanos for a set of X-rays with no hassle at all.
When the X-rays broke a few years later I replaced them with a set of Grip Shift Attack shifters that still work trouble free.
I bought a new bike this summer that came equipped with Shimano RF shifters and I do like them. I don't think that they are necessarily better than the Grip Shifts, just different, in my opinion. I also ride or have owned road bikes with Shimano STI and Campy Ergo and pretty much feel the same way. Both systems work well and it is just a personal preference thing,