I want a vape where I can just put a small amount in (just enough as I need).
A new vape to the market that I've been using for a few months now is perfect for small, measured doses. It's an upgrade (a big one) to what's maybe the original vape (patented in '78-the Eterra). I find myself using it instead of my Silver Surfer (and I'm not the only one), and that says a lot. It's the Purple-Days diffuser (it really is a legit aroma diffuser too)- purple-days.com. Some nice user reviews over at fuckcombustion.com too. This vape really is a steal at $150 IMO, and I've owned a bunch of different vapes. You'll never find another vape with this kind of build quality (including ROHS compliant parts) and time investment, at anywhere near this price. Over 80 separate steps in the build process-all hand made with a beautiful hardwood shell. You can find some vids on youtube as well, including some amazing durability tests.

And since you're concerned with efficiency, I'll agree with trance that the herbalAire is a good one (very efficient in thoroughly cooking your herb-I've used one for the last two years), but the Purple-Days beats it. Every vape loses some vapor due to condensation, if nothing else, but the P-D has very low condensation loss, never burns the bowl, and is therefore the most efficient vape I've ever used (about 15 total). Most highly recommended.