I have the standard JS MaltMill. Since I bought it (and I've changed mash tun equipment in that time) my brewhouse efficiency has been consistently 75% or higher for standard to big 5 gallon batches. Having never owned or used a 3-roller, I can't advise which would be better, but from my experience it's not worth the extra price.
The only things I've been wildly different on have occurred with my keg mash tun were a Special Bitter that came out with high OG and a 10 gallon Strong Scotch that came out around 65% efficiency. Otherwise I've hit my numbers within 3 gravity points on nearly every batch.
I've also had no issues with my rye or wheat beers being low, which is one consideration for going with adjustable or 3-roller mills.