For portable, reliable and strong hitting I recommend either the Lotus or Solo. The only problem with the Lotus is you will have to learn how to use it and then you will have to teach others during the sessions. With six people I would get exhausted teaching all night. But everyone I have taught it to gets it quickly and loves it.
As for the Solo, Vicki is right on, imo. I have the Solo, Ed's wooden stem and a regular JyARz that I hold together with a rubber band. If you pre-grind what you want into the JyARz (and it holds plenty) you can go for a long time with the Solo. With the wooden stem it is brainless and is not going to break. You just pack it and pass it. All you have to tell people is to suck on it and don't pull the stem out...good to go. I hear people all the time say the Solo is only good for one or two people, three at most. But I have consistently shown up at parties with the same group of people and effectively taken care of up to six users...two of us heavies. And they all love it and ask me to bring it.
My Solo has Centizen's after-market battery in it, which holds a lot of charge for a long time, but it is one of the older models that does not work while charging. If you get the newer model that you can use while charging, you should be good to go for as many and as long as you like (bring an extension cord for easy passing around). I consider this to be a portable desktop experience that has been a real hit with my friends. If you go to puffitup.com and use the code Solo160, you can get all this for $207 plus shipping from one place.
After I got this Solo set up and my Lotus I got rid of my other portables since they weren't getting any use.