Arial vs Helvetica, or why I will defend Arial until I'm bored doing so
If you in any sense enjoy typography you already know you have to love Helvetica and hate Arial. Hey, it's the law, I didn't come up with it.
Except… I don't buy it. Not entirely.
The common reasoning is that Microsoft ripped off Helvetica by producing a sub-standard version of it with Arial, but pretty much every part of that argument is patently false. It takes minimal research to learn Arial was a product of Monotype, not Microsoft. And to say it's a rip-off of Helvetica, well, Helvetica is a rip-off of Akzidenz-Grotesk (and earlier fonts) should we follow that logic, but I don't see too many people raise that argument. (Watch Helvetica for more on the font's history, it's streaming on Netflix.)
The differences between the two fonts can be hard to spot, even if you work regularly with them. The capital "G" and "R" are the giveaways, and "Q", "r", and "a" are helpful too. General differences in stroke cuts and glyphs can be spotted if you look closely.

But for the most part? We're talking more similarities than differences.
I do think Helvetica in and of itself is a nicer looking font, but am starting to tire of all the typography-snobs being so down on Arial. They're nearly identical. They're both inspired by older typefaces. It's not the end of the world should a website out there dare to use Arial.