4DoF is what I've been using since I got turned onto it ~4 years ago. Once properly set up, the dope is pretty spot on provided I pull my head out of my ass. There have been some features like the range cards added to it that make it extremely handy for matches. The biggest downer is if your bullet isn't in the 4DoF library, but there is still an included G1/G7 solver on board. I think the range card is $1, otherwise it's free, too.
Also to caveat on what others have said, 4DoF side of that solver is not the same behind the scenes as the other solvers. Most all of what's out there besides 4DoF and Lapua's 6DoF solvers are point mass BC solvers. Some have more intricacy to them and the ability to have multiple BC's or variable BC's through the velocity range, but they're still point mass solvers and there are some inherent (albeit sometimes very minor) errors that exist with such solvers. Where this really comes into play is the fact that BC and drag are more accurately Mach dependent, not necessarily velocity dependent. If conditions are always the same, then there is no difference, but if the temperature changes, for example, the mach number at the same velocity will change-- and that in itself will cause a BC shift (This is why 4DoF doesn't use density altitude, if anyone is wondering-- you can have the same DA at infinitely many different temperatures but the mach shift with temp is left unknown and results in errors). It may be very small, but it's there. Also, they historically don't handle aerodynamic jump especially well. A lot of the time it takes pretty serious ranges to expose these errors, and they're certainly better today than when I first started doing LR shooting in the mid 2000's.
Typically a BC solver is looking at very few inputs, BC, mass, diameter, length, maybe a couple of BC's for different velocity/mach ranges... 4DoF is has a CAD model of the bullet being used as a starting point to figure out various CoM, CoP, moments, coefficients etc.. about the physical projectile, then includes doppler recorded Cd vs. Mach data that encompass literally hundreds of inputs for each bullet in the library (This is why only 5 profiles fit on the 4DoF Kestrel). From that point it's doing a numerical physics/fluids solution that takes advantage of more of the specific physical properties of the specific bullet used in the library. Another way of thinking of it is instead of relating a 143 ELD-X to a G1 or G7 standard, 4DoF is using the "G143ELDX" standard. I don't have much experience with Lapua's 6DoF solver so I can't comment there, but of the typically used solvers I see used here in the states, 4DoF has the ability to be the most correct with correct inputs (I've used it several times, successfully, as a chronograph). I suppose 6DoF could theoretically be more accurate but I don't know how you are supposed to know 2 of those degrees of freedom. Haven't done much digging on that subject-- don't know anyone really that uses the Lapua solver.
How much any of that matters may come out in the wash depending on use-case, personal preferences, input errors, and how loose the screw behind the trigger is