And here's another one to a Wikipedia article about the usage share of the different operating systems. Here's a link to a site with some of the fonts that come pre-installed with different operating systems. This will also take some load off you server even though serving fonts isn't such a big deal. Keep in mind this is far from ideal in most cases but would allow you to avoid licensing costs and reduce the time it takes for your website to load (since it will not be downloading fonts).
HELVETICA VS HELVETICA NEUE FOR ANDROID
Your font stack could be something like font-family: "Helvetica Neue", Helvetica, Arial, sans-serif and you'd be covering the most common devices and operating systems (except for Android which I think doesn't come with any of those two font families). The name Helvetica means Swiss in Latin, and it was named that way due to its Swiss designer. Firstly, it was known as the Neue Haas Grotesk but was renamed to Helvetica later. Unfortunately Arial Narrow isn't included in iOS but, since both Helvetica and Helvetica Neue come pre-installed in all Apple devices, you wouldn't have to worry too much about it. Helvetica is a neo-grotesque font with a realist design, designed by Max Miedinger, a Swiss typeface designer. They’re generally used when you don’t want the letters to get in the way of the information. Helvetica Neue (and the original Helvetica) are known for being a bit stale. It comes pre-installed in (almost?) every Windows version and also Apple devices. Helvetica Neue was designed in 1983, and pixels weren’t a consideration back then.
HELVETICA VS HELVETICA NEUE INSTALL
When you install a TrueType font, whose name matches the PostScript font installed on this computer, Windows will not be able to distinguish between them, which can lead to a change in the font type. ttc (Helvetica Neue LT Std 85 Heavy.ttc). ttf (Helvetica Neue LT Std 85 Heavy.ttf). Unless you need something that looks almost exactly like Helvetica, Arial might be an option you should consider. fon (Helvetica Neue LT Std 85 Heavy.fon).
You may make a slim case that Arial is better. Before people jump down my throat, be aware my tongue is in cheek. I find the differences in uppercase CGQR and lowercase a and t the easiest to spot.
Everyone's been giving you names of fonts that look similar to Helvetica (some more than others) but depending on what kind of project it is that you're working on you might not need any of those. Yes, one is better than the other, for all contexts.