Saruman was a higher-ranked wizard and the leader of the White Council, while Gandalf was primarily seen as a wise warrior and counselor to Frodo. Gandalf became stronger as the White Wizard and the leader of the wizards, ultimately besting Saruman in combat due to his loyalty and growth in power and authority.
Seeing how Saruman was likely still as powerful as ever, this just goes to show how much stronger Gandalf the White had become. Unless the feats of the blue wizards become widely known and are somehow even greater, it is safe to say that Gandalf the White is the most powerful of all of Middle Earth's wizards.
Gandalf the Grey was one of at least five Istari (alongside Saruman and Radagast the Brown, and two unknown Blue Wizards). He was powerful to say the least, but the wandering wizard's abilities paled in comparison to what he'd become after defeating the Balrog.
Though wizards are technically Maiar, they do not possess all the same abilities in their wizard forms. This is why, despite Balrogs and Sauron also being Maiar, Gandalf wasn't evenly matched in his wizarding form—especially as Gandalf the Grey.
The Witch-king and Gandalf are both powerful, but Gandalf is a Maiar, making him more potent than most beings. In the extended edition for Return of the King, Gandalf struggles against the Witch-king, serving as added tension before Eowyn's victory.
As previously stated, Gandalf is a Maia and is therefore superior to Elves regarding power. Still, this isn't to say that an elf couldn't develop enough skill and power to defeat a Maia. As a bearer of one of the Three Elven Rings (Nenya), Galadriel would have an edge against Maiar like Saruman and Radagast.
Take note, then, that at the root of Gandalf's quest is fear -fear of Sauron in particular. We are not told exactly why -but Sauron is a fellow Maiar, an angelic being who chose to follow Morgoth at the beginning.
He will fight in the Last Battle against the Valar and their allies, but will ultimately be slain by Túrin Turambar, the Man he cursed. By finally defeating Morgoth, Túrin will avenge not only himself, but all members of the race of Men.
As the story progressed, it became increasingly clear that Gandalf's expertise in magic outclassed Saruman's. That became evident when Gandalf, as the White Wizard, overpowered Saruman in The Lord of the Rings: The Two Towers. That said, he certainly wasn't the better wizard in The Fellowship of the Ring.
WEAKEST: Hobbits are one of the weakest races on middle earth. Most can be defeated by simply ruining their lunch. Hobbits are charming and valuable people but not a very strong race.
Tolkien makes it clear that Gandalf and the other Istari aren't really wizards of their own accord but divine, angelic beings on a mission. Their job isn't to go around performing miraculous feats of magic, but to help those who seek to oppose evil.
In LotR, wizards can't fly or change shape. While they were immortal beings, when they became incarnate as Istari they took on human frailties as well. And their power was very limited.
Gandalf is no mere man, but a Maiar, which are essentially the equivalent of angels in Tolkien's world. Not only that, Gandalf is capable of feats of sorcery that could easily beat back the Dark Lord. Fighting the Balrog for three days and two nights makes everything else seem like a cakewalk.
In close-quarters combat, Gandalf easily has an upper hand because of the weapon he wields. Glamdring, the Elven blade he uses, would put Dumbledore in a spot of trouble. He'd need to maintain his distance at almost all times during this battle, while Gandalf would be comfortable fighting at both short and long ranges.
Gandalf by a long shot. Harry Potter is, at best, an above average wizard, whose best at disarming his enemies. Gandalf was a Maia, an angelic being. Harry Potter is just outclassed by a wide margin.
It was said that Morgoth hated and feared the House of Fingolfin most among the Houses of the sons of Finwë, especially Fingolfin's son Turgon, as it was prophesied that his doom would come from the House of Turgon.
From a technical sense, Sauron and the Balrogs were Maiar, not Valar. That meant that they were designed as lesser beings from the beginning of time. Thus, in their original forms, Morgoth would have easily defeated Sauron in a fight.
In his notes, Tolkien remarks that Sauron saw Galadriel as his equal. Add that to the fact that she's untrusting of Sauron (yes, even when he's in his Annatar guise) and an unwavering, single-minded force, and it's more likely than not that Sauron feared Galadriel — or the potential she held to upend his plans.
In general Sauron did not seem to be afraid of the Balrog during the Third Age. The behavior of Durin's Bane indicated that he would not leave Moria and its tunnels : he was not a rival for the control of Middle-earth and the Balrog did not share Sauron's abilities as a potential Dark lord.
Meanwhile, a few faithful Númenóreans, led by Elendil, were saved from the flood, and they founded Gondor and Arnor in Middle-earth. Sauron still considered them his hated enemies and he launched a pre-emptive attack on Gondor in S.A. 3429.
Despite all his strength, Smaug does have one weak spot: an open gap in his treasure armor upon his left breast. One direct hit with an arrow or sword in that specific spot, and the dragon goes down. Even without magic, as long as Gandalf has the upper hand and Smaug is distracted, he can kill the dragon in one shot.
Gandalf's main reason for supporting Thorin's quest in The Hobbit was to eliminate the threat of the dragon Smaug, who would be a powerful ally for Sauron. Despite popular belief, the Balrog known as Durin's Bane was more powerful than Smaug in Middle-earth, being a literal, primordial demon.
