A lot of good opinions, preferences, and some facts.
I bought my lathe and mill at the same time and the cash was a stretch. I opted for a smallish square column mill. The salesman said, "knowing what you are planning on doing, I don't think you are going to be happy with that small mill." I was back a week later exchanging it for the larger round column machine for the same price.
I agree with all the complaints about the round column mill. But I have workaround for the single major problem, which is loosing your zero when you move the head. As already mentioned, the points or an edge finder or dial indicator work fine and don't take too much time.
But the major trick for me is planning my work. Look at the longest and shortest tool you will be using, and like Craig said, stub drills, a few extensions, use a tall end stop for your vise, and move the part up and down in the vise when you can. If you can afford a dovetail column mill, great. If you can't, you can certainly make the round column one work for you. Just my opinion.
Lloyd