Got a set of Dominator V3 with furious true-D diversity module, and I am trying to decide on what antenna I should use. I'm running a madmushroom as a circular, this will be primarily for racing, and trying to decide on the secondary one. 

I am leaning toward the VAS 3 turn helical. Also open to a crosshair patch or a VAS double pepper box. I know everyone will have a different opinion but I hoping to get a consensus

Go for a Patch antenna, they are tiny yet gives pretty good range.

Fatshark spironet seems to be the one everyone uses.

TBS patch seems to work well too. I have a Pepperbox on my ground station, also works well. Just make sure to account for the angle of your head while flying. Some people have their antennas looking at the ground the whole time

Helical and a spironet are a great combo.. even a pepper box and a spironet... as far as the right and left aspect.. I wouldn't worry too much about it as long as you have the same direction on the quad you should get the best signal. Just remember that with a "directional" antenna, be sure not to have your head pointed down at the ground when you fly.. kinda defeats the purpose of the "directional" aspect.

I use the IBCrazy 9.5 dbic helical, excellent reception at 5.4 miles!

I have a Spironet RHCP mushroom and 8dbi mini-patch, works well. I have a helical which I used to use with my standalone diversity receiver before I got my fatsharks - it's good but very narrow beam.