the kr808 was the first one i bought, and using the easy refill method helps big time (not as messy too if u do it right) plus doing the spin thing to force the juice to the bottom of the cart after the refill works best (no gurgling), also makes it super quick to refill.
the 510 i acquired (nicstick), vapes great but the flavor sucks after a while for me (note for me), the 808 hangs in there for a good part of a day... but i cant direct drip with it as easily as i can with the 510.
my current purchases
1st setup is
kr-808 with 2 auto batteries and 10 cartomizers, plus a 30ml bottle of juice.
(Feb 15th 2010 was the day it came, i saw, and immediately vaped back to about 5 analogs a day from 2 packs a day)
2nd setup was a 510 with 1 auto battery, and a handful of carts, from a mall newsstand.
then i bought 2 more 30ml bottles of juice, 1 XL manual 808 battery as well as a 808 batt to 510 atty adapter. (thank you jesus for goodprophets tasty winston)
so now i pretty much have a great variety of vaping tools, lol
but the "No Frills" way is to go with a kr808. my wife likes the way the 510 works though, and with the 808 and 510 cart mod i did, it drags right for her and doesn't slip juice on her lips. (for when she borrows my 808)
the 510 to 808 mod, increased my Kr-808 cartomizer size and reduce the slippage from a bad refill. basically i took the cart of a 510 and slipped it into the top of 808 cartomizer to increase the chamber without looking to ridiculous at work and hold more juces, lol
(and as soon as i hit 15 posts... i post a link to the How to, lol)