Hopefully the following info helps. Please let me know if you have any more questions.
When I first started tying gamechangers I used Hareline Frizzle Chenille since it came in three sizes so you can get a correct taper without having to trim. The three sizes are, smallest to largest, medium-large-wide. *** Please note that for some reason, and no one I have talked to seems to know why, there is no such thing as the UV Pearl in the wide size. You can order it, but what you get will be the large size in a wide bag. Instead, just use the UV Pearl Green Hue which comes in all three sizes and looks nearly identical. On many of my flies I have a combo of UV Pearl and UV Pearl Green Hue and you can't tell unless you look really closely and know what you are looking for. *** The flies pictured are five shanks and one hook. I do medium on the first two shanks, large on the middle two shanks and large on the final shank and hook. With that ratio the taper comes out where it swims nicely.
The second picture down is tied with CCT (Cascade Crest Tools) Body Fur, which is the same thing as Chocklett's Body Wrap. If you have ever been to an Orvis and see the Rainbow Trout gamechanger where it looks like the colors were applied with a Sharpie, then you have seen a gamechanger tied with this material. This material is all one size and you need to trim it to shape. It also takes some practice to wrap it dense enough where it looks good.
Another material I use is Hareline Finesse Chenille (not in any of the photos), which comes in two sizes, large and medium. You can use both sizes on a fly and get something resembling a taper, but some trimming will still be required. You can also just tie with the large since you are going to have to trim the fly anyway. *** This is another one where quality control is not awesome. The materials differ depending on the color. No idea why, but if you order the minnow grey you get a nice, soft material, while if you order the black you get a wiry, stiff material. Someone I spoke with who knows a lot more than I do said he thinks it may have to do with the dye they use, but that is just a guess. Finesse Chenille also works very nicely when using it to prop up other materials such as on a feather gamechanger.
Finally the longer fly at the bottom is tied with Renzetti H2O Polar Fiber Brushes. The brushes come in three sizes, 3/4", 1 1/2" and 3". You can use the different sizes to get a pretty nice taper. I never use the 3" ones since they are really long and are probably better used on pike or musky flies, but the smaller two sizes work great. They are a bit expensive, but make a very nice fly.
I just noticed an error in the original post. The other fly in the bottom picture is tied with Frizzle Chenille, not Finesse Chenille.
Also, Flymen Fish Company posted this a few weeks ago. It has a lot of good information on it.