I have both,
my wife prefers the eGo/510 feeling I prefer the kr808...but we both use each others units
the KR808, I use smoketip brand, gives a warmer vapor...if you get an automatic definately go kr808
the eGo (I use the volcano Inferno), gives a cooler vaper..lots of it and they taste just slightly different using the same
juice..I prefer our eGo for dripping and use it for that exclusively but when I go out and about or to work I normally take the smoketip. She takes the magma's and the pcc to hold her cartomizers.
We use mostly cartomizers for both of them, I just find it easier to fill up the cartomizers the night before and wake up and grab them then fooling around with carts...I had a cart yesterday and it pulled the filler out when I removed it from the atty...not cool as my hands were kind of messy and I didn't want nicotine fingers..blah, I find cartomizers to be more consistent as well, so if I am not at home dripping on the eGo I am using cartomizers and my wife uses them as well in her standard sized 510...again just for ease of use. Plus if your atomizer dies it won't matter if you have 20 extra carts with you as you will not be able to use any of them.
Honestly I don't think you will go wrong whichever way you go...down the line you can get the other model as a back up pv anyway.