Spreadsheet - Spreadsheet script languages are made to support spreadsheets, which themselves are designed for report generation, and the processing of light amounts of data.
If you're thinking of implementing business logic here, stop. Turn off your computer, head to the closest bar, and start drinking. Don't stop until your liver revolts. I just saved you two years of trying to maintain a buggy script no one really knows how, why, (or really if,) it works. They're too fragile, and they still might trudge on in a broken state. So now you have invalid results. Hope someone noticed before it was too late. Now you have to fix the data and the script. And your liver still hasn't forgiven you.
Oh, and not only did you just lock your company on a specific platform, but also a specific version of your spreadsheet software, because we both know the next version will break your script.
Standalone - As long as you know what you're doing, you've got a decent platform, and you're not doing anything exotic like storing data in a centralized server, it'll probably be the fastest and easiest of the three options.
Downsides? You've locked your company into that platform, and the aforementioned data sharing pains. Thankfully, modern databases and database libraries elevate most of the hassle. There's also the installing and updating process.
Web - The hot trend! A web application lets you control the (server side) execution environment far better than a standalone application. Its greatest strength is its portability. You can write it once and you're able to use it on your PC, Sam can access it though is iPhone, and that jerk John can use it on his Linux box. If only you could get it looking right on Internet Explorer. And Firefox. And Opera. And Safari. And Chrome. And . . .
Downsides? Well, the obvious flaw is the centralized processing. Your multi-core computer sits idle while the overworked server processes the data. Another is the need to harden the application. What happens if John opens a telnet connection to the web server and sends invalid but properly formatted data? Because he's going to; he's a jerk.
tl;dr - Assuming you're equally competent and confident on them, go with web if you want to centralize the business logic and data, or standalone applications if you don't.
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