I have the Janty Stick, which is basically an 801 with a better, and even longer lasting rechargeable battery (and cheaper to replace), as well as a built in passthrough. I also have the 510.
Here is the thing... I love them both, for different reasons. Right now I am getting great vapor from both of them. The same flavor tastes differently on both of them because the 510 atty gets a little hotter. Some flavors taste better on the 510, some are better on the 801.
I'm actually thinking of getting the 510 adapter for the Janty Stick, that way I can switch back and forth between 801 and 510 depending on what juice I am using, and still have great battery life and a built in passthrough.
So if your main concern is larger carts and battery life, I suggest the 801, or even the Janty Stick if you can afford to pay a little bit more. And if you want to experiment with the 510 later, get the 510 adapter for the stick, and give it a shot. You may find yourself like me, and loving them both.
I hope that helps.

Feel free to shoot me a PM if you have any other questions.
Added: And just so you know, the Janty Stick is smaller than you would think it is just by looking at the pictures on the site. It's easily concealable in your hand... unless you have very tiny hands, then it's mostly concealable.

So no worries about holding something large that looks like a big power screwdriver or such.