To the original poster, I'll touch on one of the best reasons to use a 3.7v mod PV over the standard 510 3.7v batteries. With actual 3.7v of power, and a low-resistance atomizer, you can hit the coveted 8-10 watt vaping sweet spot. Regular 510 batteries are too weak for this. 6v PVs can do it, but you have to invest in regulators or pricey high voltage atomizers.
Here's some info to keep in mind when you're shopping for parts.
Batteries - research the actual voltage it puts out (the voltage level)
Atomizers - when buying, look for the ohms rating (the resistance level)
Here's a link to an Ohm's & Watt's Law Calculator
Punch in the voltage and the resistance (ohms) and click 'Calculate' and look at the resulting 'Power (watts)' level that you get.
What you're shooting for is 8-10 watts most of the time. Most users find that this is the sweet spot for vaping. If you have a PV that you enjoy using, find the voltage and ohms, punch those in, and jot down the resulting power level. It might not be between 8-10 watts, but it might be your personal sweet spot. You can shop more wisely when you can figure this stuff out before spending $$. Yay!
Examples
I have a 510 battery, it's 3.7v but doing online research I find it puts out around 3.2v. I have a 510 atomizer, rated at 2.3 ohms. So over to that calculator: 3.2volts and 2.3ohms gives me 4.4 watts of vaping power. Very poor!
Next I have a 510 battery, again puts out just 3.2v... and I have a low-resistance 510 atomizer, rated at 1.5 ohms. Calculator gives me... 6.8 watts of vaping power. Better!
Alright. Now I get a 3.7v mod, I find a battery that puts out 3.7v. I use a LR atomizer with it, which again is rated at 1.5 ohms. Calculator gives me...
9.12 watts. Perfect!
Anyway, some food for thought, happy vaping!