I am not an expert but I am in the process of getting a JD237 and I have been told that it was the last model that Deere made. It comes with a 1000 rpm pto sproket. As for comparing it to an IH 234 what I gather from reading this site it is like racing a Model T with a Nascar.
I got a 237 this year to "replace" my 227. It is the cadillac of corn pickers, thats for sure. 100 times easier to mount than an IH, and does a better job IMHO.
How does it mount? As far as I know, the 234 is the easiest to mount, IF you have the rockshaft lift. I had the cylinder lift on my picker, but i could still mount it in under an hour.