I would go for the one with the widest frequency range, most power and a plasma lamp.
That's just me.

I bought one that does not have the full range of frequencies available, so I can't recommend it because I think there are better ones out there and am currently doing my own research on them all. Here is one is one I am thinking of possibly upgrading to, but haven't finished my research yet. It appears in accordance to Dr. Royal Rife principles (see frequency generator linked by frequencyrising.com website).
It's a big investment and everyone needs to really do their own in-depth research.
Another thing that is a factor in my decision is Medbeds - so I'm dragging feet. I reckon those are like rife machines on Star Trek steroids and if they are going to be released soon, then buying one at this late stage might be moot, BUT we don't know when they will be released to the public. Lord Knows everyone needs a Medbed. I spent a significant amount on my first rife machine and don't regret it one bit, and it's a big purchase for sure. I would definitely go for the machine with the most p