In short, a lift over 4" you need to move the roll center below that either way is acceptable. From the rear brackets I've seen the poly bolt-on is the best. Matter of fact I am replacing the axle side rear bracket of my RE lift this summer with it, although I'll be welding it in place. The RE is cast and the poly is steel beef.
The poly frame side reinforcement brackets are great but, not really needed unless you need/want beef. The adjustable track bar will allow you dial in the axle placement. In the rear being off a little does not hurt.
I have copy/pasted a reply I made some months ago to a guy with a very similar question about roll center of a vehicle. The comments about bracket and space really apply to the front end; in the rear the best way to do it is with a quality axle side bracket....IMO
Here are my thoughts on the issue you ask about. I do want to clarify I am an Electrical engineer not a mechanical or automotive. For your reference you can read a pdf at this link...(you may want some asprin after reading it)
But I will try to briefly explain the concept and how is applies directly to your question.
The "roll center" is more crucial in a high speed situation; you have more lateral force (sideways) at high speed than in low speed, or no speed, situation. Obviously, our JKs are not high speed units.
The most crucial measurement is the angle but, the SAE defines it as a height. In plain English, the more angle the track bar has the more likely the vehicle is to roll (let me finish). The best is to have the track bar and the axle on the same plane; this is the most rigid set-up. Great then just add brackets, right?? NO...The brackets have disadvantages like increasing the leverage of the force; this is why they are prone to fail. Also, if you bracket down or up the tack bar then, you (may) decrease the amount of suspension travel available.
So in a nut shell, when you raise a vehicle to improve off-road capability you DECREASE on-road. This is the nature of the beast. So, what we do is compromise. Unless you go with a heavy duty bracket that will not fail it is better to have an adjustable track bar. But, once you get over a certain height (because the higher you go the more increase in angle of the track bar) you do need brackets.
To recap, the problem with brackets is they are more likely to bend or break and only have a set-measurement or, a rough adjustment if there are multiple mounting holes. An adjustable track bar allows for fine adjustment.
I'll go back to your post.... the proper wording would be “a bracket lowers the angle of roll center and a longer track bar increase the angle". The rub is if we increase the angle it will allow for more articulation but decrease stability.
Here is the answer to your question “is there a difference in handling or ‘Roll Center’ be using a bracket vs track bar?” for OUR application under 4" of lift a longer adjustable track bar is better, over 4" you need to buy heavy duty bracket AND have an adjustable track bar. The key is with less than 4" the roll center angle of just a longer track bar is in an acceptable range for our usage.