The answer to this question will come down to each person's individual preference for the functionality of a sci-fi super weapon. If one considers the sheer might of the Starkiller Base and nothing else, then it is clear that the Starkiller Base is the better of the two.
Is the Starkiller Base more powerful than the Death Star?
With a huge battery to focus its power, the massive base could wipe out entire systems with better efficiency than the Death Star. But where the Death Star left little time for its victims to realize what happened, one function made Starkiller Base's deadly weapon more terrifying than its predecessor.
The Empire constructed the first Death Star in secret for nearly two decades before using it to destroy Alderaan; the second Death Star boasted a more powerful superlaser, with improved targeting sensors and power regulators.
Starkiller Base was a First Order military base located on the ice planet of Ilum in the Unknown Regions. Commanded by an unofficial triumvirate of General Armitage Hux, Kylo Ren, and Captain Phasma, it was armed with a superweapon capable of destroying entire star systems halfway across the galaxy.
How many planets can Starkiller Base destroy at once?
The first Death Star only managed to destroy Alderaan before the Rebellion took it down, and the Second Death Star didn't get the chance to destroy any planets. However, Starkiller Base was able to destroy five whole planets in the Hosnian system—including Hosnian Prime.
Both bases could take each other out, but the Death Star might actually be the better of the two thanks to its higher functionality and more reliable fuel source in relation to the power it requires.
During the match, Luke remarks that Starkiller was making him angry, and when Luke is then defeated by Starkiller, who mocks him on destroying him as he "destroyed his father", Luke screams in anger and falls to the the dark side as Fallen Luke.
Lord Starkiller is an antagonist in an alternate Star Wars timeline in which Darth Vader is defeated and killed by his former apprentice Galen Marek, code named Starkiller.
As for Starkiller (Galen Malek), he was an exceptional Force user. In terms of general power, he was more powerful then Windu and Kenobi, less so then Anakin.
The Death Star's most famous weakness was its thermal exhaust port, but Star Wars has hinted the battle-station had another critical weakness that would have become clear over years. Emperor Palpatine intended the Death Star to be almost invincible, but he had not factored in Galen Erso's sabotage.
Leia brought the plans to the Alliance leadership on Yavin 4, who quickly analyzed the data and discovered the design flaw deliberately left in the battle station by Imperial engineer Galen Erso, which would allow a single proton torpedo, fired into the thermal exhaust port, to destroy the entire station.
Out of the 2 billion inhabitants on Alderaan - with the modern-day populations of China and India having about 2.8 billion people combined - about 60,000 survived the destruction of the planet due to being outside of its star system at the time.
Galen Marek, better known as Starkiller, was the main protagonist of the Legends games before Disney bought Lucasfilm. He displayed incredible control of the Force, from moving a Star Destroyer to defeating both Vader and Palpatine in succession.
It's a common misconception that 17 year-old Starkiller/Galen Marrek was MORE powerful than Darth Vader. He wasn't. There were two big factors in Starkiller's victory against Vader: He was his teacher.
It is also outright stated that Sidious was feigning weakness to goad Starkiller into striking him down and to turn him to the Dark Side. He didn't beat Sidious. He even went oneness and then died to Sidious.
That said, considering Star Wars: The Force Unleashed's power levels, Starkiller is arguably more powerful than most Jedi who ever appeared in a live-action or animated Star Wars project. Players actually get to defeat Palpatine in The Force Unleashed, and Galen Marek's very existence was a threat to the Emperor.
In the real universe, Luke became a Jedi, Redeemed his father, and lived happily ever after. BUT, in the Ultimate Sith Edition, he fought Lord Starkiller on Hoth and turned to the Dark Side.
Starkiller shot Force Lightning at him and ended the fight as he threw his lightsaber at him, splitting Kylo Ren into two and launched his remains out of the base.
The fight itself is a draw, but Yoda turns it into a victory for Sidious by retreating (because they are evenly matched and there is nothing more he can do then and there).
Starkiller's not more powerful than Vader. He is more diverse in his repertoire of Force techniques, but essentially, Starkiller is all flash and no substance. To give you an idea of what I'm talking about: if Force Lightning from Palpatine is a 10, Starkiller is at a 6, maybe a 7.
A notable Jar'Kai master was the Priapulin Jedi Master Skwelli, who carried six lightsabers. He was renowned for his skill in his era, and recordings of his fighting form were considered a wonder to behold.
In a galaxy filled with lightsabers of various colours, the Darksaber stands out as the rarest lightsaber colour, shrouded in mystery and steeped in history. Created by the first Mandalorian Jedi, it has passed through the hands of warriors, terrorists, and heroes, leaving an indelible mark on the Star Wars universe.
The Darksaber. The only black blade-like Saber ever made, constructed with fine Beskar, by the only Mandalorian to ever become a Jedi in the Order's entire history.
