I've got hundreds of dollars of equipment that now sits in drawers as 'backup' equipment. What I've found myself using for the last couple of months are 650mah eGo Twists, and the Vision replaceable head products (vivi nova, it's mini version, and the 'stardust' version.)
I like the 650mah Twist for the size, not the battery capacity, but it lasts me the day most of the time. I cant stand the extra inch or so of length on the biggest one, because it sometimes falls out of my shirt pocket. I guess I'd prefer a bigger diameter battery over a longer one if I want more battery capacity.
The Mini Vivi Nova is my favorite delivery device. Capacity is adequate, but it's not nearly as heavy as the full-sized one. They both perform well with stock heads, but really take off when rebuilt to my liking with cotton or bamboo thread wicks, and they are pretty easy for me to rebuild.
I also like the cheap 'phoenix' rebuildable dripping atomizer that's hit the scene recently, but it could definitely benefit from some improvements, which do seem to be coming very soon.