I like a rear grip of 7"-7.5", which I know is longer than most. I also like the rear grip to be pretty much a uniform 1 1/8" in diameter with a mushroom but cap, and again I know this is larger than most like.
For the foregrip, I like a slight taper from reel seat to mid-grip and then a very gradual taper to the front of the grip with the grip being close to 1.25" at its widest in the mid-grip area with a diameter of around .75" at the front of it next to the rod blank. This profile is basically a very long and larger diameter version of the old half-wells style single-hand grip. I also like my foregrips to be between 14" and 18" long depending on rod length and line size. I also prefer to have my reel seats mounted so they are downlocking on a 2-hand rod so the reel weight is a little bit closer to the end of the rod to help ballance it.
Good quality cork (even though it is a bit pricey at around $2.00/ring or more) is the material I prefer to build my grips out of. Also I build my grips on the rod blank itself by gluing the rings to the blank and each other, then turning the grips the next day after the glue has dried. I really don't like the preformed grips for 2-handed rods because they are too short and too small a diameter for my tastes and I prefer a fairly large diameter grip.
I have seen some very nice grips that use burl cork for part of the grip and a few nice ones that had foam grip material in the grip along with natural cork.