Likes:
G10
Micarta
Wood
Dislikes:
Polished/buffed handles
Anything that doesn't fall into these categories fits into my ambivalence category.
As some have said, it depends on the knife and how the handle is finished by the maker. In folders I am a big fan of Spyderco's FRN, because the shape they give it is both grippy and comfortable. Even though I have largely taken myself out of the folder acquisition game I will be making an exception for a Resilience lightweight with blue FRN scales.
From a maker's perspective, my favorite is G10, because it is the easiest handle material to work and finish for me. It's also
usually available for less cost than similar Micarta. From a user perspective, it is either micarta, or textured G10, because micarta is grippiest, and ever gripper when wet, and G10, while not particularly grippy, becomes more than grippy enough with texture. By the way, by textured I don't mean peel ply as used in production folders. While this is also good, that texture tends to smooth out and lose its grip over time. I mean textured by a craftsman who takes grip, comfort and function into consideration. Here are some examples of textured G10 knives I made.
Note the edges of the scales are radiused in order to preserve comfort. In fact, this is one advantage G10 has over micarta, in that the radiused scale edges of G10, being smoother than Micarta's more porous feel, are always more comfortable at the same finish, or even at a lower grit finish than Micarta. This is what makes G10 feel more slippery as well, but when textured, you get the best of both words.
The other issue with G10 is it is a bit heavier than Micarta, so the simple fix for me there is on a knife where this would potentially hinder optimal balance, I simply hollow out a portion of the inside of the scales, which combined with texturing, reduces the weight to even lighter than untextured, unhollowed Micarta scales would be. I have swung large choppers and machetes at length that I had given textured G10 handles, and found their retention more than adequate, even during rainfall.
And G10 gives more options for color combinations than Micarta, at least from what I have been able to find available.
All that being said, I do very much love Micarta as well.