Capt45, can I ask what sort of projects you have in mind for this machine? If you have to do bigger stuff then something like a PM 25 might not be practical.
On another thread, we were just discussing the amount of working room available on a PM 25 and it amounts to about 10". Fill that with a vise that is 3-4" tall and now you're looking at 6" of working room. Something to think about.
There are a few other considerations, mostly mass and rigidity. The bigger and more rigid, the better. An RF-30/31 weighs about 800#, heavier than three PM25's put together. Just the head alone is over 200#. I think most folks who pooh pooh these round column mills have never run one or even seen one in the flesh. It is a big machine to be sitting on a bench. It is pretty rigid for its size and is plenty capable for most hobby shops, I think.
The round column is an issue that is hardly ever a real issue. An RF-31 has a 3" diameter quill with 5" of travel. If you space the head to accommodate the longest tool you will use for your project you do not need to move the head at all. Look at the field and you will not find many with as big a quill or as much quill travel.
An RF machine can be made to run pretty accurately. As
@Dudemanrod said, upgrading the spindle and drive sleeve bearings on an older machine can accurize the quill quite nicely. I'm not sure of his run out but mine is just under 0.0001", which is comparable or better than most new mills on the hobby market. Add the weight, mass, quill travel and low cost to that and it is a package that is tough to beat for the price.
Just food for thought.