On various occasions, Data remarks that Geordi is his best friend onboard the Enterprise. Does Geordi think the same of Data? Somehow I think that Geordi would consider a fellow human to be his best friend, but I am not certain.
Does anything in canon answer this question?
There is plenty of evidence to suggest Geordi can have a best friend that is artificial.
Data and Geordi have a close relationship, for sure. During the development of TNG, the characters had a kinship because they both saw the world differently than the other crew. Here's a clip from a Gizmodo intervew with LeVar Burton.
We noticed that Geordi was often the character who seemed to identify with cyborgs and robots the most. He's close friends with Data, and when Hugh the Borg comes aboard the Enterprise, Geordi is the first character to reach out to him. So we wondered if Burton thought that Geordi saw himself as a cyborg. Burton responds:
No, not at all. But — and this is little-known Trek lore — in the audition sides for the character, during the casting process, there was a scene that Gene Roddenberry wrote between Geordi and Data, that established their relationship. And in that scene, Geordi and Data discussed how Geordi's eyes and Data's brain saw the world in a very similar way. They saw the truth of the world around them. And so, in the scene that Gene wrote, they formed a team, and they called themselves the Perceivers, because their perceptions were alike.
And even though the Perceivers thing never made it to the pilot episode, the relationship between Geordi and Data certainly did. And I think that that aspect of Geordi that sees the world around him in a much more truthful manner, and his vision as he interprets it through the VISOR — there's a way that he interprets the world and sees the world slightly differently than the other humans around him, which I think gives him more compassion. That's the one thing I hear from people more than anyone else — that they get that Geordi is a little looser than everybody else, and that he's really more accepting. And I think that accessibility comes from his compassion.
Geordi La Forge's profile in the DK factbook The Star Trek Book bluntly identifies Data as being Geordi's closest friend.
Close friendships
The android, Data, was La Forge’s closest friend, and the pair often worked on engineering problems together. La Forge made it his personal mission to help Data in his quest to understand what it means to be Human. The pair often role-played in holodeck simulations of Sherlock Holmes stories, with Data assuming the role of Holmes and La Forge playing Dr. Watson.
By the Canon, as ensign on the U.S.S. Victory, he was saved from a parasite infection on Tarchannen IV and only his close friendship with another crewmate Susanna Leitjen saved him; so here is someone who should be his best friend. However, the best friend of Geordi is Data according to most of the records.
According to the canonical Star Trek: The Next Generation Writer/Director's Guide on the entry about Geordi:
His closest friend is Data, and the two of them are particularly efficient when working together on away missions pg 7
