I had previously owned a cheap vaporizer, it had a copper heating plate glass dome and a tube to suck on. It was unpredictable, was not super effecient, and I broke the glass dome. I have since then bought a volcano (retail+postage=ouch) and it's so good I bought one for a family members birthday.
I like the volcano as once the bag is full it is portable, it's effecient (agree with the 1/3 as above) though it can be cumbersome as you need to plug it in, set it up etc. If you don't travel with it then it shouldn't be a problem and I highly recommend it!
My lungs cleared up within the week, the weed tastes amazing, you don't reek of smoke nor does your house. Oh and it may be placebo but I find the high more intense. On the down side it isn't very portable, they're expensive to buy (I've made my money back in 3 months) and you don't get quite the hit if you use a vaporizer without a bag (which is why I also suggest volcano)