Until we know of the official height difference between Luke and Bigger Luke, we can't say this for sure.
Actually since he's not even human and from a different galaxy possibly billions of years ago he may not even be comparable relevant height one way or another....
assuming that Han is about six feet tall though and the two users are of equal skill then high ground is unbeatable (I didn't make these rules! - even though Darth Maul has the high ground to beat all high ground when Anakin does him in...) and the Plasma sword has the potentially exploitable advantage of the split blades to "catch" a light saber I still would give it to the plasma sword....
EXCEPT!!! Plasma Sword in most campaign settings takes damage/depletes energy and eventually sputters out if it makes high energy contact with mass (flesh, armor, vehicles etc) - without extensive testing in real life conditions- it's not possible to know if the contained plasma blade will take meaningful damage from the saber's assembly of "photonic molecules." It's possible that the saber's field generated "fake" massy properties will not meaningfully deplete the Energy Sword - and potentially even augment its kinetic impact as a kind of resonant reflection.
this is made more complex by the recent revelation of Forerunner "hard light " technology which uses a different and more advanced technology to imbue photons with useful mass like properties- including far better control over heat and rigidity down to the subatomic level- no clumsy EM fields for Forerunner tech - however the Covenant- while reverse engineering many forerunner concepts from found artifacts- are doing so at a fairly rudimentary level- and humans have shown a far better ability to analyze, replicate and even improve upon both covenant and forerunner tech - a natural ability amplified by our willingness to grant AIs agency and the freedom to innovate- covenant religious and cultural traditions restrict AI to mete obedient number crunching and navigation chores.
now - Force users? Trickier still. Jedi can for example use the Force to enhance their weapon skill of course- but also do stuff like protect their skin from excess heat radiation (trade federation ship scene where they melt the bulkhead door) - Elites can't use the Force- but several humans- Chief included- have exhibited mysterious interactions with dormant and active Forerunner tech - potentially related to an unusual property of their dna- either predicted by or possibly manipulated by long vanished forerunner biologists. Could that be expressed as a surfeit of modichlorians? (Which I have head canoned as a measurable
side effect of force power- bacteria like "moths" attracted to a flame and not the CAUSE of the force like some weird old Star Wars enthusiasts insist) I think we have to consider that possibility.
In summary then, the Plasma or Energy Sword is, in every possible rational scenario- more powerful and deadly therefore than a light saber. Even a light saber stacked with a thousand dead Jedi Khyber derived "red crystals "
if a Star Wars enthusiast here knows
more about the saber (my knowledge is f Star Wars is pretty rudimentary) and presents a contradictory fact, I will simply drive to the office and add newly "discovered " information that leapfrogs any such contradiction. So no matter what, Plasma Sword wins.
I rest my case.