Most people consider ceramic heating elements to be the safest in the industry. I would not give the heating element type any consideration in either one of these models. They both do what they do very well. Smokless, I think the answer for you will come down to how you expect to use the vaporizer and hwo much you want to spend. It cannot be ignored that the Extreme (E) is half the price of a Volcano (V).
I've used a V and been around it, but never owned one...just couldn't afford it. The E was my first vaporizer, and I still use it today (last night in fact). I say that because I have five or six different brands of vaporizers, and it is important that the E still gets used and is not relegated to collect dust. It is very versatile. Here's my opinion of the two as your only vaporizer:
1 -- durability. The V wins this hands-down. The E has several glass parts that can and do break. This is because most people prefer glass. The good thing about the E that makes up for this is that you will never be disappointed in their customer service. When things go wrong they make it right.
2 -- delivery. No question the V has the best bag system on the market. I prefer the easy-valve system to the E's bag system any day. This is 100% related to ease of use and has nothing to do with vapor quality.
3 -- vapor quality. I don't have side-by-side experience with the V, but others have said they are in the same arena. The bigger difference here is that with the V you only get bags, and therein lies the answer to your vapor-to-air ratio. Bags are bags and they mix the beginning of a bowl with the middle and last so that your vapor experience is homogeneous. The E gives the option of using the whip. Any direct draw system allows you to enjoy the best first hits along with their better taste and thickness. Once I got the hang of the whip I loved it and rarely go back to bags.
4 -- environment. Do you mostly vape in private or parties? The V is the ultimate party vape, but not as good for solitary sessions as the E, imo. I used th E for a party the other day and manned it myself as I was not going to let a bunch of fucked up newbies break or misuse my E. I think the V would worry me less in that area. Do you have kids or other unwanted eyes around your vape? I can hide my E in the closet and sneak away for quick whip hits, but wouldn't use its bag system or the V's bags for stealth...too long and noisy creating the bags.
In general, if your wanting a durable party vape that you could easily resell and recoup your investment if you don't like vaping, and if money is no obstacle, get the V. No one with any brains is going to tell you the V sucks. It's just overpriced.
If you want something that is a little more stealthy and has lots of options while not breaking the bank, get the E. I like the versatility of the E and it gets a lot more use from me since I have the whip option. If I had a bag only vape, it wouldn't get much use with the other options I have around here.