This is [obviously] only my personal opinion. But if I vaped only at 3.7v, I would choose the Icon. It's the perfect size for on-the-go use, especially if you want to put your PV in a front shirt pocket, as I do at work (a corporate environment). The relatively shorter battery life is offset by the fact that 14500s are so much smaller than 17670s, it's no big deal to put one or two spare ones in your pocket or bag.
I realize the V3 is smaller than the Silver Bullet, Omega, or most other tube mods out there. And I have used mine quite a bit when I'm out and about. But I always migrate back to my Icon for use outside of the house.
It all boils down to personal preference and usage habits. As Cash said, they both perform the same at 3.7v. The difference is small size/needing to carry spare batteries or larger size that will last pretty much all day with one battery.