Best rear suspension for drag/street handling
Depends entirely on your budget and plans for the car.
A set of 130 lb/in leaf springs with an adjustable rear sway bar is what some of the best handling mopars out there right now run.
Otherwise you’re just looking at various conversions- triangulated 4 links, true 4 links, 3 links, or the QA1 6 link. All have their issues and advantages.
Triangulated 4 link is probably the “easiest”, as in there are a few kits available. They retain most of the factory locations for stuff like the exhaust and fuel tank. But their adjustability isn’t actually a massive improvement, and they can limit travel a little depending on the layout.
A true 4 link would be more adjustable, but it would also mess with the factory location of things (like the entire back seat most likely). And you’d be building it yourself.
A 3 link is by far the most adjustable, and is favored by a lot of road racers. But again, this has issues with the factory locations of significant parts. There is a kit, XV Engineering makes it (one of the former people from XV motorsports). I don’t know much about the install beyond generalities, like usually the fuel tank location has to be moved. But yeah, probably the best from a handling and adjustability stand point. XV VTR REAR SUSPENSION A, B and E Body
And then there’s the QA1 6 link. It bolts in, uses all the factory locations for everything. Including the spring hangers, which limits tire width. And then there’s the suspension travel, which is significantly reduced.
Compared to what you’re getting for what you’re spending, unless you’re building an all out road racing car a set of good leaf springs and an adjustable sway bar will take you the furthest.
Nothing against HemiDenny either, but all you get from a coilover conversion is a rack and pinion and more header room. It does not improve handling compared to a well set up torsion bar suspension. Which costs a ton less. And you can have a very well handling car with a torsion bar suspension.