My experience with the Shimano Revo Shifters are that they are more cheaply made than the Sram ones, but work better. There may be a difference in robustness of construction or in durablity, but neither are very good in this regard.
I do not like the Sram gripshifters - at least the SHimano compatible ones - I have no experience with the ones meant for Sram derailleurs. My experience with Shimano compatibleStram gripshifters is similar to yours in terms of the less good feel than the Shimano.