A lot seems to depend on what's popular in your particular area.
Having said that, around here, it's JD, Vermeer or NH. Those three make up probably 90% of all round balers in our area. All three are good machines. I bought a JD, because I got a great deal on a good clean used one. If I had to go buy a new baler, it would have probably been a Vermeer.
Vermeer 504M Classic
I have a JD 457. (458 is the current model, see here:
JD 458) It makes a 4' wide x 5' tall roll. If I do my part, it will make a really nice, tight roll that weighs about 1000-1200 lbs. It uses hydraulic tension. That really helps keep the roll tight, from center to outside edge. Tight rolls hold their shape and stack well.
Just my preference, but I don't have the net wrap, and don't want it. It has to be cut from the roll before feeding. Now, net wrap is faster that wrapping a roll with twine.
On the JD, I would suggest the "Mega-Wide" pickup. Much more forgiving when picking up the windrow. On the Vermeer, the "HaySaver" wheels help to do the same thing. I also like the big "flotation" tires. If you have a cab tractor, I would look for a model with the electronic monitor.
If you're looking for a good used baler, you'll have to do some homework. You really need to talk to someone in your area that is using one and knows how to operate it. They can show you all the "wear parts" and what to look for. It's a long list. For instance, are the chains riding high on the sprocket teeth? That means that the chains are worn (stretched) and need to be replaced. Depending on wear, the sprockets may need replacing also. New chains and sprockets can easily cost hundreds of dollars. Are the belts worn and torn? A new set of belts will run well over $1000. You get the picture.