Apple - A modern and faster alternative to Disk Inventory X

OmniGroup offers a free utility called OmniDisksweeper which lists files/folders sorted by size.

OmniDiskSweeper is really great at what it does: showing you the files on your drive, in descending order by size, and letting you delete them easily! It scans your disks as quickly as possible and shows you the facts — if a file doesn't make the cut to stay, just click the big Delete button and be done with it. It's a fast, easy way to find those large files cluttering up your drive and clearing them out for new, better things. Make sure you want them gone, though. There's no going back

Starting with macOS Sierra, macOS comes with an built in app from Apple called Storage Management, which is a part of the System Information app. In different tabs it shows you the largest apps installed, as well as a folder viewer with their sizes listed. A special tab shows the largest files over all of your folders, which I find very practical.

To launch Storage Management open Spotlight Search by hitting ⌘ Command Space, type "Storage Management" and hit ⏎ Return.

Pros:

• Free,
• Fast,
• Provided by Apple, so it knows what it's doing.

You can find more information here.

I think Disk Inventory is as fast or slow as any of the others. If the disk is big, it's slower than on a little one, and of course, on an SSD it is really fast. Although it is from 2006, I think it isn't bad coded, and it still works on my 10.9.

It gives more info than you need, but you can ignore that, as long as you find what you need. I guess what takes time is the reading of the disc, an app without the details of kind of info won't, as far as I think, really take much less.

I am using it for ages now, there was a time in Mavericks it didn't work, now it goes well. I recommend GrandPerspective, it seems to make the same (with more alternatives which you anyhow don't seem to need), but is fresher .

GrandPerspective: http://grandperspectiv.sourceforge.net